diff --git a/locales/ar-SA/opencadstudio.ftl b/locales/ar-SA/opencadstudio.ftl
index f54eb5651..7130e80c8 100644
--- a/locales/ar-SA/opencadstudio.ftl
+++ b/locales/ar-SA/opencadstudio.ftl
@@ -5026,6 +5026,9 @@ plot =
     .fit-to-paper = ملاءمة للورق
     .layout-plots-the-current-sheet-using-the-selec = يطبع التخطيط الورقة الحالية باستخدام حجم الورق المحدد.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = دمج الخطوط المتداخلة
     .object-lineweights = سماكات خطوط الكائنات
     .orientation = الاتجاه
diff --git a/locales/bg-BG/opencadstudio.ftl b/locales/bg-BG/opencadstudio.ftl
index 4cd537a82..a24eb249c 100644
--- a/locales/bg-BG/opencadstudio.ftl
+++ b/locales/bg-BG/opencadstudio.ftl
@@ -5014,6 +5014,9 @@ plot =
     .fit-to-paper = Побери в хартията
     .layout-plots-the-current-sheet-using-the-selec = Оформлението плотира текущия лист, използвайки избрания размер хартия.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Обедини припокриващи се линии
     .object-lineweights = Дебелини на линии на обект
     .orientation = Ориентация
diff --git a/locales/cs-CZ/opencadstudio.ftl b/locales/cs-CZ/opencadstudio.ftl
index cd37022e6..7d7364d18 100644
--- a/locales/cs-CZ/opencadstudio.ftl
+++ b/locales/cs-CZ/opencadstudio.ftl
@@ -5011,6 +5011,9 @@ plot =
     .fit-to-paper = Přizpůsobit papíru
     .layout-plots-the-current-sheet-using-the-selec = Rozvržení vykreslí aktuální list pomocí zvolené velikosti papíru.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Sloučit překrývající se čáry
     .object-lineweights = Tloušťky čar objektů
     .orientation = Orientace
diff --git a/locales/de-DE/opencadstudio.ftl b/locales/de-DE/opencadstudio.ftl
index e41fa3534..2612d5f56 100644
--- a/locales/de-DE/opencadstudio.ftl
+++ b/locales/de-DE/opencadstudio.ftl
@@ -5012,6 +5012,9 @@ plot =
     .fit-to-paper = An Papier anpassen
     .layout-plots-the-current-sheet-using-the-selec = Das Layout plottet das aktuelle Blatt mit dem ausgewählten Papierformat.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Zusammenführung überlappender Leitungen
     .object-lineweights = Objektliniengewichte
     .orientation = Ausrichtung
diff --git a/locales/el-GR/opencadstudio.ftl b/locales/el-GR/opencadstudio.ftl
index 5911988ce..a5664898f 100644
--- a/locales/el-GR/opencadstudio.ftl
+++ b/locales/el-GR/opencadstudio.ftl
@@ -5014,6 +5014,9 @@ plot =
     .fit-to-paper = Προσαρμογή στο χαρτί
     .layout-plots-the-current-sheet-using-the-selec = Η επιλογή Διάταξη εκτυπώνει το τρέχον φύλλο με το επιλεγμένο μέγεθος χαρτιού.
     .sheet-sizes-and-printable-areas-reported-by-th = Μεγέθη φύλλων και εκτυπώσιμες περιοχές όπως τα αναφέρει ο εκτυπωτής.
+    .custom-paper-size = Προσαρμοσμένο μέγεθος χαρτιού
+    .printable-margins = Εκτυπώσιμα περιθώρια
+    .enter-a-positive-width-and-height = Δώστε θετικό πλάτος και ύψος.
     .merge-overlapping-lines = Συγχώνευση επικαλυπτόμενων γραμμών
     .object-lineweights = Πάχη γραμμών αντικειμένων
     .orientation = Προσανατολισμός
diff --git a/locales/en-US/opencadstudio.ftl b/locales/en-US/opencadstudio.ftl
index eddfd0028..dbcc88cd7 100644
--- a/locales/en-US/opencadstudio.ftl
+++ b/locales/en-US/opencadstudio.ftl
@@ -5015,6 +5015,9 @@ plot =
     .fit-to-paper = Fit to paper
     .layout-plots-the-current-sheet-using-the-selec = Layout plots the current sheet using the selected paper size.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Merge overlapping lines
     .object-lineweights = Object lineweights
     .orientation = Orientation
diff --git a/locales/es-ES/opencadstudio.ftl b/locales/es-ES/opencadstudio.ftl
index 2a52f63aa..8faefd7a0 100644
--- a/locales/es-ES/opencadstudio.ftl
+++ b/locales/es-ES/opencadstudio.ftl
@@ -5014,6 +5014,9 @@ plot =
     .fit-to-paper = Ajustar al papel
     .layout-plots-the-current-sheet-using-the-selec = La presentación traza la hoja actual con el tamaño de papel seleccionado.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Fusionar líneas solapadas
     .object-lineweights = Grosores de línea de objetos
     .orientation = Orientación
diff --git a/locales/fi-FI/opencadstudio.ftl b/locales/fi-FI/opencadstudio.ftl
index e3fbfd865..9de9ec986 100644
--- a/locales/fi-FI/opencadstudio.ftl
+++ b/locales/fi-FI/opencadstudio.ftl
@@ -5013,6 +5013,9 @@ plot =
     .fit-to-paper = Sovita paperille
     .layout-plots-the-current-sheet-using-the-selec = Asettelu piirtää nykyisen arkin käyttämällä valittua paperikokoa.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Yhdistä päällekkäiset rivit
     .object-lineweights = Objektin viivan painot
     .orientation = Suuntautuminen
diff --git a/locales/fr-FR/opencadstudio.ftl b/locales/fr-FR/opencadstudio.ftl
index 0cbfa07b4..c2e716831 100644
--- a/locales/fr-FR/opencadstudio.ftl
+++ b/locales/fr-FR/opencadstudio.ftl
@@ -5014,6 +5014,9 @@ plot =
     .fit-to-paper = Ajuster au papier
     .layout-plots-the-current-sheet-using-the-selec = La présentation trace la feuille courante avec le format de papier sélectionné.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Fusionner les lignes qui se chevauchent
     .object-lineweights = Poids de ligne d'objet
     .orientation = Orientation
diff --git a/locales/hi-IN/opencadstudio.ftl b/locales/hi-IN/opencadstudio.ftl
index 5a2a4f100..6e34cface 100644
--- a/locales/hi-IN/opencadstudio.ftl
+++ b/locales/hi-IN/opencadstudio.ftl
@@ -5002,6 +5002,9 @@ plot =
     .fit-to-paper = कागज़ पर फ़िट करें
     .layout-plots-the-current-sheet-using-the-selec = लेआउट चयनित कागज़ आकार पर वर्तमान शीट प्लॉट करता है।
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = मर्ज ओवरलैपिंग लाइन
     .object-lineweights = ऑब्जेक्ट लाइनवेट
     .orientation = अभिविन्यास
diff --git a/locales/hu-HU/opencadstudio.ftl b/locales/hu-HU/opencadstudio.ftl
index 5222d1072..b204a6052 100644
--- a/locales/hu-HU/opencadstudio.ftl
+++ b/locales/hu-HU/opencadstudio.ftl
@@ -5013,6 +5013,9 @@ plot =
     .fit-to-paper = Papírra illeszthető
     .layout-plots-the-current-sheet-using-the-selec = Az Elrendezés az aktuális lapot a kiválasztott papírmérettel ábrázolja.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Egyesítse az átfedő vonalakat
     .object-lineweights = Objektumvonalvastagságok
     .orientation = Tájékozódás
diff --git a/locales/it-IT/opencadstudio.ftl b/locales/it-IT/opencadstudio.ftl
index d5277f8b7..68d841798 100644
--- a/locales/it-IT/opencadstudio.ftl
+++ b/locales/it-IT/opencadstudio.ftl
@@ -5013,6 +5013,9 @@ plot =
     .fit-to-paper = Adatta alla carta
     .layout-plots-the-current-sheet-using-the-selec = Layout traccia il foglio corrente utilizzando il formato carta selezionato.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Unisci linee sovrapposte
     .object-lineweights = Spessori linea degli oggetti
     .orientation = Orientamento
diff --git a/locales/ja-JP/opencadstudio.ftl b/locales/ja-JP/opencadstudio.ftl
index 4d85663b0..6bf94b41a 100644
--- a/locales/ja-JP/opencadstudio.ftl
+++ b/locales/ja-JP/opencadstudio.ftl
@@ -5002,6 +5002,9 @@ plot =
     .fit-to-paper = 用紙にフィット
     .layout-plots-the-current-sheet-using-the-selec = 選択した用紙サイズで現在のシートを印刷します。
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = 重複線を結合
     .object-lineweights = オブジェクトの線の太さ
     .orientation = 方向
diff --git a/locales/ko-KR/opencadstudio.ftl b/locales/ko-KR/opencadstudio.ftl
index 22cb62a7c..a79acfaa8 100644
--- a/locales/ko-KR/opencadstudio.ftl
+++ b/locales/ko-KR/opencadstudio.ftl
@@ -5013,6 +5013,9 @@ plot =
     .fit-to-paper = 종이에 맞추기
     .layout-plots-the-current-sheet-using-the-selec = 레이아웃은 선택한 용지 크기를 사용하여 현재 시트를 플롯합니다.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = 겹치는 선 병합
     .object-lineweights = 객체 선가중치
     .orientation = 오리엔테이션
diff --git a/locales/nl-NL/opencadstudio.ftl b/locales/nl-NL/opencadstudio.ftl
index 7cd127c2f..4a7bbc633 100644
--- a/locales/nl-NL/opencadstudio.ftl
+++ b/locales/nl-NL/opencadstudio.ftl
@@ -5012,6 +5012,9 @@ plot =
     .fit-to-paper = Aan papier aanpassen
     .layout-plots-the-current-sheet-using-the-selec = De lay-out plot het huidige vel op het geselecteerde papierformaat.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Overlaplijnen samenvoegen
     .object-lineweights = Objectlijndiktes
     .orientation = Oriëntatie
diff --git a/locales/pl-PL/opencadstudio.ftl b/locales/pl-PL/opencadstudio.ftl
index c215855f1..ede80253e 100644
--- a/locales/pl-PL/opencadstudio.ftl
+++ b/locales/pl-PL/opencadstudio.ftl
@@ -5013,6 +5013,9 @@ plot =
     .fit-to-paper = Dopasuj do papieru
     .layout-plots-the-current-sheet-using-the-selec = Układ drukuje bieżący arkusz przy użyciu wybranego rozmiaru papieru.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Połącz nakładające się linie
     .object-lineweights = Szerokości linii obiektu
     .orientation = Orientacja
diff --git a/locales/pt-BR/opencadstudio.ftl b/locales/pt-BR/opencadstudio.ftl
index 5e306b0ea..68e04964a 100644
--- a/locales/pt-BR/opencadstudio.ftl
+++ b/locales/pt-BR/opencadstudio.ftl
@@ -5014,6 +5014,9 @@ plot =
     .fit-to-paper = Ajustar ao papel
     .layout-plots-the-current-sheet-using-the-selec = Layout plota a folha atual usando o tamanho de papel selecionado.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Mesclar linhas sobrepostas
     .object-lineweights = Espessuras de linha dos objetos
     .orientation = Orientação
diff --git a/locales/ru-RU/opencadstudio.ftl b/locales/ru-RU/opencadstudio.ftl
index 92727daae..cbd2bfe63 100644
--- a/locales/ru-RU/opencadstudio.ftl
+++ b/locales/ru-RU/opencadstudio.ftl
@@ -5015,6 +5015,9 @@ plot =
     .fit-to-paper = Вписать в лист
     .layout-plots-the-current-sheet-using-the-selec = Лист печатается на выбранном формате бумаги.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Слияние пересекающихся линий
     .object-lineweights = Весы для объектов
     .orientation = Ориентация
diff --git a/locales/tr-TR/opencadstudio.ftl b/locales/tr-TR/opencadstudio.ftl
index f24afc924..954050cba 100644
--- a/locales/tr-TR/opencadstudio.ftl
+++ b/locales/tr-TR/opencadstudio.ftl
@@ -4954,6 +4954,9 @@ plot =
     .fit-to-paper = Kağıda sığdır
     .layout-plots-the-current-sheet-using-the-selec = Yerleşim, geçerli sayfayı seçilen kağıt boyutuyla çizer.
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = Çakışan çizgileri birleştir
     .object-lineweights = Nesne çizgi kalınlıkları
     .orientation = Yönelim
diff --git a/locales/zh-CN/opencadstudio.ftl b/locales/zh-CN/opencadstudio.ftl
index 34bc20fc7..97d63c729 100644
--- a/locales/zh-CN/opencadstudio.ftl
+++ b/locales/zh-CN/opencadstudio.ftl
@@ -4997,6 +4997,9 @@ plot =
     .fit-to-paper = 布满图纸
     .layout-plots-the-current-sheet-using-the-selec = 布局使用所选纸张尺寸打印当前图纸。
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = 合并重叠线
     .object-lineweights = 对象线宽
     .orientation = 方向
diff --git a/locales/zh-TW/opencadstudio.ftl b/locales/zh-TW/opencadstudio.ftl
index 49f85db3c..63ffd2c16 100644
--- a/locales/zh-TW/opencadstudio.ftl
+++ b/locales/zh-TW/opencadstudio.ftl
@@ -5009,6 +5009,9 @@ plot =
     .fit-to-paper = 布滿圖紙
     .layout-plots-the-current-sheet-using-the-selec = 配置使用所選紙張尺寸列印目前圖紙。
     .sheet-sizes-and-printable-areas-reported-by-th = Sheet sizes and printable areas reported by the printer.
+    .custom-paper-size = Custom paper size
+    .printable-margins = Printable margins
+    .enter-a-positive-width-and-height = Enter a positive width and height.
     .merge-overlapping-lines = 合併重疊線
     .object-lineweights = 物件線寬
     .orientation = 方向
diff --git a/src/app/update/file.rs b/src/app/update/file.rs
index 463d4f5d4..6ac933b02 100644
--- a/src/app/update/file.rs
+++ b/src/app/update/file.rs
@@ -197,7 +197,7 @@ fn margins_for_settings(
     if paper_unchanged(d, stored) && stored_device == device {
         return stored.margins;
     }
-    let margins = device.margins_mm(&plot_dialog_paper(d));
+    let margins = device.margins_mm(&plot_dialog_paper(d), &d.custom_papers);
     acadrust::objects::PaperMargin::new(margins.left, margins.bottom, margins.right, margins.top)
 }
 
@@ -3855,6 +3855,86 @@ impl OpenCADStudio {
         )
     }
 
+    /// The inline custom-sheet editor of the Plot dialog. A sheet is added
+    /// to (or replaced in) the persisted list under its media name and
+    /// selected at once; the list is saved immediately so it survives a
+    /// crash the way a plotter configuration would.
+    fn on_custom_paper_msg(&mut self, msg: crate::ui::window::plot::CustomPaperMsg) {
+        use crate::ui::window::plot::{CustomPaperDraft, CustomPaperMsg as C, MarginSide};
+        let d = &mut self.plot_dialog;
+        match msg {
+            C::Open => {
+                let paper = plot_dialog_paper(d);
+                let existing = d
+                    .custom_papers
+                    .iter()
+                    .find(|custom| custom.canonical() == paper.canonical);
+                let margins = match existing {
+                    Some(custom) => custom.margins_mm(),
+                    None => plot_dialog_device(d).margins_mm(&paper, &d.custom_papers),
+                };
+                let mut draft = CustomPaperDraft::from_paper(&paper, margins);
+                // A catalogue sheet is only the starting size; the new sheet
+                // gets its own name (AutoCAD's generic one when left blank).
+                if existing.is_none() {
+                    draft.name.clear();
+                }
+                d.custom_editor = Some(draft);
+            }
+            C::Cancel => d.custom_editor = None,
+            C::Name(value) => Self::edit_custom_draft(d, |draft| draft.name = value),
+            C::Width(value) => Self::edit_custom_draft(d, |draft| draft.width = value),
+            C::Height(value) => Self::edit_custom_draft(d, |draft| draft.height = value),
+            C::Units(value) => Self::edit_custom_draft(d, |draft| draft.inches = value == "Inches"),
+            C::Margin(side, value) => Self::edit_custom_draft(d, |draft| {
+                let index = match side {
+                    MarginSide::Left => 0,
+                    MarginSide::Bottom => 1,
+                    MarginSide::Right => 2,
+                    MarginSide::Top => 3,
+                };
+                draft.margins[index] = value;
+            }),
+            C::Add => {
+                let Some(draft) = d.custom_editor.as_mut() else {
+                    return;
+                };
+                match draft.build() {
+                    Ok(custom) => {
+                        let canonical = custom.canonical();
+                        d.custom_papers.retain(|existing| existing.canonical() != canonical);
+                        d.custom_papers.push(custom);
+                        d.custom_editor = None;
+                        d.paper = canonical;
+                        let (w, h) = plot_dialog_sheet_mm(d);
+                        d.paper_width_mm = w;
+                        d.paper_height_mm = h;
+                        self.save_config();
+                    }
+                    Err(error) => draft.error = Some(error),
+                }
+            }
+            C::Remove => {
+                let selected = plot_dialog_paper(d).canonical.into_owned();
+                let before = d.custom_papers.len();
+                d.custom_papers.retain(|custom| custom.canonical() != selected);
+                if d.custom_papers.len() != before {
+                    self.save_config();
+                }
+            }
+        }
+    }
+
+    fn edit_custom_draft(
+        d: &mut crate::ui::window::plot::PlotDialogState,
+        edit: impl FnOnce(&mut crate::ui::window::plot::CustomPaperDraft),
+    ) {
+        if let Some(draft) = d.custom_editor.as_mut() {
+            edit(draft);
+            draft.error = None;
+        }
+    }
+
     fn normalize_common_plot_dialog(&mut self) {
         self.plot_dialog.center = true;
         self.plot_dialog.offset_x = "0.0".into();
@@ -3895,6 +3975,10 @@ impl OpenCADStudio {
                 }
                 Task::none()
             }
+            M::CustomPaper(msg) => {
+                self.on_custom_paper_msg(msg);
+                Task::none()
+            }
             M::PrinterProperties => {
                 match crate::io::print_to_printer::open_printer_properties(
                     self.plot_dialog.printer.as_deref(),
@@ -5077,6 +5161,65 @@ mod plot_paper_tests {
         assert!(app.plot_dialog.printer_media.is_none());
     }
 
+    #[test]
+    fn a_custom_sheet_is_added_selected_persisted_and_written_with_its_margins() {
+        use crate::ui::window::plot::{CustomPaperMsg as C, MarginSide};
+        let mut app = app_with_printer_named_sheet();
+        let _ = app.on_plot_dialog_open();
+        let _ = app.on_plot_dlg(PlotDlgMsg::Printer(crate::ui::window::plot::OUT_PDF.into()));
+        let custom = |m: C| PlotDlgMsg::CustomPaper(m);
+        let _ = app.on_plot_dlg(custom(C::Open));
+        // Seeded from the selected ISO A4 on the PDF driver, nameless.
+        let draft = app.plot_dialog.custom_editor.clone().expect("editor open");
+        assert_eq!((draft.width.as_str(), draft.height.as_str()), ("210", "297"));
+        assert_eq!(draft.margins, ["5", "17", "6", "18"]);
+        assert!(draft.name.is_empty());
+        let _ = app.on_plot_dlg(custom(C::Name("Roll 24".into())));
+        let _ = app.on_plot_dlg(custom(C::Width("1500".into())));
+        let _ = app.on_plot_dlg(custom(C::Height("609.6".into())));
+        let _ = app.on_plot_dlg(custom(C::Margin(MarginSide::Left, "3".into())));
+        let _ = app.on_plot_dlg(custom(C::Margin(MarginSide::Top, "4".into())));
+        let _ = app.on_plot_dlg(custom(C::Add));
+        assert!(app.plot_dialog.custom_editor.is_none(), "Add closes the editor");
+        assert_eq!(app.plot_dialog.paper, "Roll_24_(609.60_x_1500.00_MM)");
+        assert_eq!(super::plot_dialog_sheet_mm(&app.plot_dialog), (1500.0, 609.6));
+        assert_eq!(app.current_config().plot.custom_papers.len(), 1, "persisted in the plot config");
+        let _ = app.on_plot_dlg(PlotDlgMsg::SetCurrent);
+        let ps = app.tabs[app.active_tab].scene.plot_settings_for("Layout1").unwrap();
+        assert_eq!(ps.paper_size, "Roll_24_(609.60_x_1500.00_MM)");
+        assert_eq!((ps.paper_width, ps.paper_height), (1500.0, 609.6));
+        assert_eq!(ps.margins, acadrust::objects::PaperMargin::new(3.0, 17.0, 6.0, 4.0));
+        // Re-adding the same size replaces the definition instead of duplicating it.
+        let _ = app.on_plot_dlg(custom(C::Open));
+        assert_eq!(app.plot_dialog.custom_editor.as_ref().map(|d| d.name.as_str()), Some("Roll 24"));
+        let _ = app.on_plot_dlg(custom(C::Margin(MarginSide::Left, "9".into())));
+        let _ = app.on_plot_dlg(custom(C::Add));
+        assert_eq!(app.plot_dialog.custom_papers.len(), 1);
+        assert_eq!(app.plot_dialog.custom_papers[0].margins.left, 9.0);
+        // Remove drops the definition; the sheet itself stays selectable.
+        let _ = app.on_plot_dlg(custom(C::Remove));
+        assert!(app.plot_dialog.custom_papers.is_empty());
+        assert_eq!(app.plot_dialog.paper, "Roll_24_(609.60_x_1500.00_MM)");
+    }
+
+    #[test]
+    fn an_invalid_custom_sheet_is_refused_with_a_reason() {
+        use crate::ui::window::plot::{CustomPaperError, CustomPaperMsg as C};
+        let mut app = app_with_printer_named_sheet();
+        let _ = app.on_plot_dialog_open();
+        let _ = app.on_plot_dlg(PlotDlgMsg::CustomPaper(C::Open));
+        let _ = app.on_plot_dlg(PlotDlgMsg::CustomPaper(C::Width("-5".into())));
+        let _ = app.on_plot_dlg(PlotDlgMsg::CustomPaper(C::Add));
+        let draft = app.plot_dialog.custom_editor.as_ref().expect("editor stays open");
+        assert_eq!(draft.error, Some(CustomPaperError::Size));
+        assert!(app.plot_dialog.custom_papers.is_empty());
+        // Typing again clears the message.
+        let _ = app.on_plot_dlg(PlotDlgMsg::CustomPaper(C::Width("500".into())));
+        assert!(app.plot_dialog.custom_editor.as_ref().unwrap().error.is_none());
+        let _ = app.on_plot_dlg(PlotDlgMsg::CustomPaper(C::Cancel));
+        assert!(app.plot_dialog.custom_editor.is_none());
+    }
+
     #[test]
     fn an_unknown_sheet_from_a_drawing_keeps_its_own_dimensions() {
         let mut app = app_with_printer_named_sheet();
diff --git a/src/io/paper_catalog.rs b/src/io/paper_catalog.rs
index 04e7164ee..1532b2354 100644
--- a/src/io/paper_catalog.rs
+++ b/src/io/paper_catalog.rs
@@ -16,7 +16,7 @@ use std::sync::OnceLock;
 
 /// Unit the media is defined in. AutoCAD keeps ISO/JIS sheets in millimetres
 /// and ANSI/ARCH sheets in inches, and the unit is part of the media name.
-#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash, serde::Serialize, serde::Deserialize)]
 pub enum PaperUnits {
     Millimeters,
     Inches,
@@ -107,6 +107,88 @@ pub enum Orientation {
     Landscape,
 }
 
+/// Unprintable margins of a sheet, in the order AutoCAD stores them. The unit
+/// is whatever the context says — millimetres in a drawing, the sheet's own
+/// unit in a user-defined size.
+#[derive(Clone, Copy, Debug, PartialEq, serde::Serialize, serde::Deserialize)]
+pub struct Margins {
+    pub left: f64,
+    pub bottom: f64,
+    pub right: f64,
+    pub top: f64,
+}
+
+impl Margins {
+    pub const ZERO: Margins = Margins {
+        left: 0.0,
+        bottom: 0.0,
+        right: 0.0,
+        top: 0.0,
+    };
+
+    pub const fn uniform(value: f64) -> Self {
+        Margins {
+            left: value,
+            bottom: value,
+            right: value,
+            top: value,
+        }
+    }
+
+    /// The same margins expressed in millimetres when they were given in
+    /// `units`.
+    pub fn to_mm(self, units: PaperUnits) -> Self {
+        Margins {
+            left: units.to_mm(self.left),
+            bottom: units.to_mm(self.bottom),
+            right: units.to_mm(self.right),
+            top: units.to_mm(self.top),
+        }
+    }
+}
+
+/// A sheet the user defined, kept in the application settings the way
+/// AutoCAD keeps custom sizes in a plotter configuration: a name, the
+/// dimensions in the sheet's own unit, and the printable margins.
+#[derive(Clone, Debug, PartialEq, serde::Serialize, serde::Deserialize)]
+#[serde(default)]
+pub struct CustomPaper {
+    /// Human name, e.g. `Roll 24`; becomes `Roll_24_(…)` in the media name.
+    pub name: String,
+    pub width: f64,
+    pub height: f64,
+    pub units: PaperUnits,
+    /// Unprintable margins in `units`.
+    pub margins: Margins,
+}
+
+impl Default for CustomPaper {
+    fn default() -> Self {
+        Self {
+            name: String::new(),
+            width: 0.0,
+            height: 0.0,
+            units: PaperUnits::Millimeters,
+            margins: Margins::ZERO,
+        }
+    }
+}
+
+impl CustomPaper {
+    /// The catalogue sheet this definition describes.
+    pub fn paper(&self) -> PaperSize {
+        PaperSize::custom_named(&self.name, self.width, self.height, self.units)
+    }
+
+    pub fn canonical(&self) -> String {
+        self.paper().canonical.into_owned()
+    }
+
+    pub fn margins_mm(&self) -> Margins {
+        self.margins.to_mm(self.units)
+    }
+}
+
 /// One sheet of the catalogue, or a sheet reconstructed from a media name.
 #[derive(Clone, PartialEq, Debug)]
 pub struct PaperSize {
@@ -156,18 +238,43 @@ impl PaperSize {
     /// in the plot dialog (`UserDefinedMetric_(420.00_x_297.00_MM)`). The
     /// dimensions are normalised to portrait so the name stays canonical.
     pub fn custom(width: f64, height: f64, units: PaperUnits) -> Self {
+        let label = match units {
+            PaperUnits::Millimeters => "UserDefinedMetric",
+            PaperUnits::Inches => "UserDefinedInches",
+        };
+        Self::custom_named(label, width, height, units)
+    }
+
+    /// A user-defined sheet under its own name, the way a plotter
+    /// configuration's custom sizes are named (`Roll_24_(609.60_x_1500.00_MM)`).
+    /// A blank name falls back to AutoCAD's generic one; spaces become
+    /// underscores in the media name and parentheses are dropped so the name
+    /// stays parseable.
+    pub fn custom_named(name: &str, width: f64, height: f64, units: PaperUnits) -> Self {
         let (width, height) = if width <= height {
             (width, height)
         } else {
             (height, width)
         };
-        let label = match units {
-            PaperUnits::Millimeters => "UserDefinedMetric",
-            PaperUnits::Inches => "UserDefinedInches",
-        };
+        let cleaned: String = name
+            .trim()
+            .chars()
+            .filter(|c| !matches!(c, '(' | ')'))
+            .collect::<String>()
+            .split_whitespace()
+            .collect::<Vec<_>>()
+            .join(" ");
+        if cleaned.is_empty() {
+            return Self::custom(width, height, units);
+        }
         Self {
-            canonical: Cow::Owned(canonical_name(label, width, height, units)),
-            label: Cow::Borrowed(label),
+            canonical: Cow::Owned(canonical_name(
+                &cleaned.replace(' ', "_"),
+                width,
+                height,
+                units,
+            )),
+            label: Cow::Owned(cleaned),
             series: PaperSeries::Other,
             variant: PaperVariant::Standard,
             width,
@@ -688,6 +795,39 @@ mod tests {
         assert_eq!(default_paper().canonical, a4().canonical);
     }
 
+    #[test]
+    fn user_defined_sheets_carry_their_name_and_margins() {
+        let roll = CustomPaper {
+            name: "Roll 24 (long)".into(),
+            width: 1500.0,
+            height: 609.6,
+            units: PaperUnits::Millimeters,
+            margins: Margins {
+                left: 5.0,
+                bottom: 17.0,
+                right: 6.0,
+                top: 18.0,
+            },
+        };
+        assert_eq!(roll.canonical(), "Roll_24_long_(609.60_x_1500.00_MM)");
+        assert_eq!(roll.paper().label, "Roll 24 long");
+        assert_eq!(roll.paper().display(), "Roll 24 long (609.6 × 1500 mm)");
+        // Round-trips through the parser like any AutoCAD name.
+        assert_eq!(
+            resolve(&roll.canonical()).unwrap().portrait_mm(),
+            (609.6, 1500.0)
+        );
+        let arch = CustomPaper {
+            name: String::new(),
+            width: 30.0,
+            height: 42.0,
+            units: PaperUnits::Inches,
+            margins: Margins::uniform(0.25),
+        };
+        assert_eq!(arch.canonical(), "UserDefinedInches_(30.00_x_42.00_Inches)");
+        assert_eq!(arch.margins_mm(), Margins::uniform(6.35));
+    }
+
     #[test]
     fn fit_centers_and_scales_within_margin() {
         // 100×100 window onto a 210×297 sheet, Fit. Limiting axis is width:
diff --git a/src/io/plot_device.rs b/src/io/plot_device.rs
index ac652f899..670e5218b 100644
--- a/src/io/plot_device.rs
+++ b/src/io/plot_device.rs
@@ -15,7 +15,8 @@
 //! a fixed table; a CUPS printer reports its media and margins over IPP
 //! (`media-col-database`), which is queried once per printer and cached.
 
-use crate::io::paper_catalog::{self, PaperSize, PaperUnits, PaperVariant};
+pub use crate::io::paper_catalog::Margins;
+use crate::io::paper_catalog::{self, CustomPaper, PaperSize, PaperUnits, PaperVariant};
 use std::collections::HashMap;
 use std::sync::{Arc, Mutex, OnceLock};
 
@@ -73,51 +74,23 @@ impl PlotDevice {
     }
 
     /// Unprintable margins the device imposes on `paper`, in millimetres.
-    pub fn margins_mm(&self, paper: &PaperSize) -> Margins {
+    /// A sheet the user defined carries its own margins for every device,
+    /// the way a custom size in a plotter configuration does; a printer that
+    /// reports the same size still wins, since it knows its hardware.
+    pub fn margins_mm(&self, paper: &PaperSize, custom: &[CustomPaper]) -> Margins {
+        let user_defined = custom
+            .iter()
+            .find(|c| c.canonical() == paper.canonical)
+            .map(CustomPaper::margins_mm);
         match self {
-            PlotDevice::Pdf => pdf_margins_mm(paper),
-            PlotDevice::Printer(name) => printer_margins_mm(name, paper),
+            PlotDevice::Pdf => user_defined.unwrap_or_else(|| pdf_margins_mm(paper)),
+            PlotDevice::Printer(name) => cached_printer_capabilities(name)
+                .and_then(|caps| caps.margins_for(paper))
+                .or(user_defined)
+                .unwrap_or(Margins::ZERO),
             // No device: AutoCAD keeps the margins of the last device or its
             // defaults; without one we show the full sheet as printable.
-            PlotDevice::None => Margins::ZERO,
-        }
-    }
-}
-
-/// Unprintable margins in millimetres, in the order AutoCAD stores them.
-#[derive(Clone, Copy, Debug, PartialEq)]
-pub struct Margins {
-    pub left: f64,
-    pub bottom: f64,
-    pub right: f64,
-    pub top: f64,
-}
-
-impl Margins {
-    pub const ZERO: Margins = Margins {
-        left: 0.0,
-        bottom: 0.0,
-        right: 0.0,
-        top: 0.0,
-    };
-
-    pub const fn uniform(value: f64) -> Self {
-        Margins {
-            left: value,
-            bottom: value,
-            right: value,
-            top: value,
-        }
-    }
-
-    /// The same margins expressed in millimetres when they were given in
-    /// `units`.
-    pub fn to_mm(self, units: PaperUnits) -> Self {
-        Margins {
-            left: units.to_mm(self.left),
-            bottom: units.to_mm(self.bottom),
-            right: units.to_mm(self.right),
-            top: units.to_mm(self.top),
+            PlotDevice::None => user_defined.unwrap_or(Margins::ZERO),
         }
     }
 }
@@ -234,12 +207,6 @@ pub fn printer_capabilities(printer: &str) -> Option<Arc<PrinterCapabilities>> {
     Some(caps)
 }
 
-fn printer_margins_mm(printer: &str, paper: &PaperSize) -> Margins {
-    cached_printer_capabilities(printer)
-        .and_then(|caps| caps.margins_for(paper))
-        .unwrap_or(Margins::ZERO)
-}
-
 /// Name of the system default printer, when the platform reports one.
 #[cfg(all(not(target_arch = "wasm32"), not(target_os = "windows")))]
 pub fn default_printer_name() -> Option<String> {
@@ -459,7 +426,8 @@ mod tests {
 
     #[test]
     fn pdf_margins_follow_autocad_per_family_and_variant() {
-        let m = |name: &str| PlotDevice::Pdf.margins_mm(&paper_catalog::resolve(name).unwrap());
+        let m =
+            |name: &str| PlotDevice::Pdf.margins_mm(&paper_catalog::resolve(name).unwrap(), &[]);
         // ISO sheets share one millimetre set regardless of size.
         let iso_standard = Margins {
             left: 5.0,
@@ -517,12 +485,49 @@ mod tests {
             inch(0.03, 0.03, 0.03, 0.03)
         ));
         assert_eq!(
-            PlotDevice::None
-                .margins_mm(&paper_catalog::resolve("ISO_A4_(210.00_x_297.00_MM)").unwrap()),
+            PlotDevice::None.margins_mm(
+                &paper_catalog::resolve("ISO_A4_(210.00_x_297.00_MM)").unwrap(),
+                &[]
+            ),
             Margins::ZERO
         );
     }
 
+    #[test]
+    fn user_defined_sheets_bring_their_own_margins() {
+        let roll = CustomPaper {
+            name: "Roll".into(),
+            width: 900.0,
+            height: 1200.0,
+            units: PaperUnits::Millimeters,
+            margins: Margins::uniform(3.0),
+        };
+        let paper = roll.paper();
+        assert_eq!(
+            PlotDevice::Pdf.margins_mm(&paper, &[roll.clone()]),
+            Margins::uniform(3.0)
+        );
+        assert_eq!(
+            PlotDevice::None.margins_mm(&paper, &[roll.clone()]),
+            Margins::uniform(3.0)
+        );
+        // An unknown printer falls back to the user's margins too.
+        assert_eq!(
+            PlotDevice::Printer("Nowhere".into()).margins_mm(&paper, &[roll]),
+            Margins::uniform(3.0)
+        );
+        // Without a definition a custom-looking sheet gets the family set.
+        assert_eq!(
+            PlotDevice::Pdf.margins_mm(&paper, &[]),
+            Margins {
+                left: 5.0,
+                bottom: 17.0,
+                right: 6.0,
+                top: 18.0
+            }
+        );
+    }
+
     #[test]
     fn ipp_media_parses_sizes_margins_borderless_and_default() {
         let caps = parse_ipp_media(IPP_SAMPLE).expect("media parsed");
diff --git a/src/locale_catalog.rs b/src/locale_catalog.rs
index 4ae3bd537..576363792 100644
--- a/src/locale_catalog.rs
+++ b/src/locale_catalog.rs
@@ -1457,6 +1457,9 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Layout name cannot be empty." => Some(("common", "layout-name-cannot-be-empty")),
         "Layout plots the current sheet using the selected paper size." => Some(("plot", "layout-plots-the-current-sheet-using-the-selec")),
         "Sheet sizes and printable areas reported by the printer." => Some(("plot", "sheet-sizes-and-printable-areas-reported-by-th")),
+        "Custom paper size" => Some(("plot", "custom-paper-size")),
+        "Printable margins" => Some(("plot", "printable-margins")),
+        "Enter a positive width and height." => Some(("plot", "enter-a-positive-width-and-height")),
         "Layout renamed: '{old_name}' → '{new_name}'" => Some(("common", "layout-renamed-old-name-new-name")),
         "Layouts" => Some(("layout", "layouts")),
         "Leader" => Some(("common", "leader")),
diff --git a/src/ui/style/form.rs b/src/ui/style/form.rs
new file mode 100644
index 000000000..cc9eff39b
--- /dev/null
+++ b/src/ui/style/form.rs
@@ -0,0 +1,206 @@
+//! Form building blocks shared by the in-canvas dialogs.
+//!
+//! The Plot dialog grew its own `label : control` rows, field and button
+//! styles, and section dividers; every dialog that followed copied them. They
+//! live here once so a new dialog reads like the existing ones and a theme
+//! tweak lands everywhere.
+
+use crate::app::Message;
+use crate::ui::style::common::muted_style;
+use iced::widget::{button, container, pick_list, row, text, text_input, Space};
+use iced::{Background, Border, Element, Length, Theme};
+use std::borrow::Cow;
+
+/// Width of the label column in a `label : control` row.
+pub const LABEL_WIDTH: f32 = 92.0;
+
+/// Dialog button: accent (primary action) or neutral.
+pub fn button_style(accent: bool) -> impl Fn(&Theme, button::Status) -> button::Style {
+    move |theme: &Theme, status| {
+        let palette = theme.palette();
+        let pair = match (accent, status) {
+            (true, button::Status::Hovered | button::Status::Pressed) => palette.primary.strong,
+            (false, button::Status::Hovered | button::Status::Pressed) => palette.background.strong,
+            (true, _) => palette.primary.base,
+            _ => palette.background.weak,
+        };
+        button::Style {
+            background: Some(Background::Color(pair.color)),
+            text_color: pair.text,
+            border: Border {
+                color: palette.background.neutral.color,
+                width: 1.0,
+                radius: 4.0.into(),
+            },
+            shadow: iced::Shadow::default(),
+            snap: false,
+        }
+    }
+}
+
+/// Text field: base background, neutral border that turns primary on focus.
+pub fn field_style(theme: &Theme, status: text_input::Status) -> text_input::Style {
+    let palette = theme.palette();
+    let border = match status {
+        text_input::Status::Focused { .. } => palette.primary.base.color,
+        _ => palette.background.neutral.color,
+    };
+    text_input::Style {
+        background: Background::Color(palette.background.base.color),
+        border: Border {
+            color: border,
+            width: 1.0,
+            radius: 3.0.into(),
+        },
+        icon: palette.background.base.text,
+        placeholder: palette.background.base.text.scale_alpha(0.48),
+        value: palette.background.base.text,
+        selection: palette.primary.base.color.scale_alpha(0.5),
+    }
+}
+
+/// One-pixel horizontal rule.
+pub fn hdivider<'a>(width: Length) -> Element<'a, Message> {
+    container(Space::new().width(width).height(1))
+        .width(width)
+        .height(1)
+        .style(|theme: &Theme| container::Style {
+            background: Some(Background::Color(theme.palette().background.neutral.color)),
+            ..Default::default()
+        })
+        .into()
+}
+
+/// One-pixel vertical rule.
+pub fn vseparator<'a>(height: Length) -> Element<'a, Message> {
+    container(Space::new().width(1).height(height))
+        .width(1)
+        .height(height)
+        .style(|theme: &Theme| container::Style {
+            background: Some(Background::Color(theme.palette().background.neutral.color)),
+            ..Default::default()
+        })
+        .into()
+}
+
+/// Muted section heading.
+pub fn section_label<'a>(label: Cow<'static, str>) -> Element<'a, Message> {
+    text(label).size(11).style(muted_style).into()
+}
+
+fn row_label<'a>(label: Cow<'static, str>) -> Element<'a, Message> {
+    text(label)
+        .size(11)
+        .style(muted_style)
+        .width(LABEL_WIDTH)
+        .into()
+}
+
+/// A `label : dropdown` row.
+pub fn labeled_pick_list<'a, T>(
+    label: Cow<'static, str>,
+    options: Vec<T>,
+    selected: Option<T>,
+    on_select: impl Fn(T) -> Message + 'a,
+    width: Length,
+) -> Element<'a, Message>
+where
+    T: ToString + Clone + PartialEq + 'a,
+{
+    let list = pick_list(selected, options, |value| value.to_string())
+        .on_select(on_select)
+        .text_size(12)
+        .padding([3, 6])
+        .width(width);
+    row![row_label(label), list]
+        .spacing(8)
+        .align_y(iced::Center)
+        .into()
+}
+
+/// A `label : dropdown` row that renders read-only when `enabled` is false.
+pub fn labeled_pick_list_enabled<'a, T>(
+    label: Cow<'static, str>,
+    options: Vec<T>,
+    selected: Option<T>,
+    on_select: impl Fn(T) -> Message + 'a,
+    width: Length,
+    enabled: bool,
+) -> Element<'a, Message>
+where
+    T: ToString + Clone + PartialEq + 'a,
+{
+    if enabled {
+        return labeled_pick_list(label, options, selected, on_select, width);
+    }
+    row![
+        row_label(label),
+        crate::ui::read_only::field(
+            selected
+                .map(|choice| choice.to_string())
+                .unwrap_or_default()
+                .as_str(),
+            12.0,
+            width,
+        ),
+    ]
+    .spacing(8)
+    .align_y(iced::Center)
+    .into()
+}
+
+/// A `label : text field` row.
+pub fn labeled_field<'a>(
+    label: Cow<'static, str>,
+    value: &'a str,
+    on_input: impl Fn(String) -> Message + 'a,
+    width: f32,
+) -> Element<'a, Message> {
+    row![
+        row_label(label),
+        text_input("", value)
+            .on_input(on_input)
+            .style(field_style)
+            .size(12)
+            .width(width),
+    ]
+    .spacing(8)
+    .align_y(iced::Center)
+    .into()
+}
+
+/// A `label : text field` row that renders read-only when `enabled` is false.
+pub fn labeled_field_enabled<'a>(
+    label: Cow<'static, str>,
+    value: &'a str,
+    on_input: impl Fn(String) -> Message + 'a,
+    width: f32,
+    enabled: bool,
+) -> Element<'a, Message> {
+    if enabled {
+        return labeled_field(label, value, on_input, width);
+    }
+    row![
+        row_label(label),
+        crate::ui::read_only::field(value, 12.0, Length::Fixed(width)),
+    ]
+    .spacing(8)
+    .align_y(iced::Center)
+    .into()
+}
+
+/// A short unlabeled text field for a compact multi-value row (`L B R T`).
+pub fn compact_field<'a>(
+    placeholder: &'a str,
+    value: &'a str,
+    on_input: impl Fn(String) -> Message + 'a,
+    width: f32,
+) -> Element<'a, Message> {
+    text_input(placeholder, value)
+        .on_input(on_input)
+        .style(field_style)
+        .size(12)
+        .padding([3, 6])
+        .width(width)
+        .into()
+}
diff --git a/src/ui/style/mod.rs b/src/ui/style/mod.rs
index f8c3fa3c7..2a86accac 100644
--- a/src/ui/style/mod.rs
+++ b/src/ui/style/mod.rs
@@ -10,6 +10,7 @@ pub mod scale_manager;
 pub mod anno_object_scale;
 pub mod style_manager;
 pub mod common;
+pub mod form;
 
 #[cfg(test)]
 mod common_tests {
diff --git a/src/ui/window/plot.rs b/src/ui/window/plot.rs
index ee6064326..24712901e 100644
--- a/src/ui/window/plot.rs
+++ b/src/ui/window/plot.rs
@@ -5,8 +5,10 @@
 //! PDF. Styled to match the other OCS dialogs (dark pills + fields).
 
 use crate::app::Message;
-use crate::io::paper_catalog::{self, PaperSize};
+use crate::io::paper_catalog::{self, CustomPaper, Margins, PaperSize, PaperUnits};
 use crate::io::plot_device::PrinterCapabilities;
+use crate::ui::style::common::muted_style;
+use crate::ui::style::form;
 use iced::widget::{
     button, checkbox, column, container, mouse_area, row, scrollable, text, text_input,
     Space,
@@ -75,7 +77,45 @@ impl fmt::Display for PlotChoice {
 
 #[cfg(test)]
 mod tests {
-    use super::PlotChoice;
+    use super::{CustomPaperDraft, CustomPaperError, PlotChoice};
+    use crate::io::paper_catalog::{resolve, Margins, PaperUnits};
+
+    #[test]
+    fn custom_sheet_draft_validates_and_builds() {
+        let mut draft = CustomPaperDraft {
+            name: "  Roll 24  ".into(),
+            width: "1500".into(),
+            height: "609,6".into(),
+            inches: false,
+            margins: ["5".into(), "17".into(), "".into(), "abc".into()],
+            error: None,
+        };
+        let custom = draft.build().expect("valid sheet");
+        assert_eq!(custom.name, "Roll 24");
+        assert_eq!((custom.width, custom.height), (1500.0, 609.6));
+        assert_eq!(custom.units, PaperUnits::Millimeters);
+        // Blank or unparsable margins mean no margin, never a refusal.
+        assert_eq!(custom.margins, Margins { left: 5.0, bottom: 17.0, right: 0.0, top: 0.0 });
+        assert_eq!(custom.canonical(), "Roll_24_(609.60_x_1500.00_MM)");
+        draft.width = "0".into();
+        assert_eq!(draft.build().unwrap_err(), CustomPaperError::Size);
+        draft.width = "x".into();
+        assert_eq!(draft.build().unwrap_err(), CustomPaperError::Size);
+    }
+
+    #[test]
+    fn custom_sheet_draft_seeds_from_a_sheet_in_its_own_unit() {
+        let arch_d = resolve("ARCH_D_(24.00_x_36.00_Inches)").unwrap();
+        let draft = CustomPaperDraft::from_paper(&arch_d, Margins::uniform(6.35));
+        assert_eq!(draft.name, "ARCH D");
+        assert_eq!((draft.width.as_str(), draft.height.as_str()), ("24", "36"));
+        assert!(draft.inches);
+        assert_eq!(draft.margins, ["0.25", "0.25", "0.25", "0.25"]);
+        let a4 = resolve("ISO_A4_(210.00_x_297.00_MM)").unwrap();
+        let draft = CustomPaperDraft::from_paper(&a4, Margins { left: 5.0, bottom: 17.0, right: 6.0, top: 18.0 });
+        assert!(!draft.inches);
+        assert_eq!(draft.margins, ["5", "17", "6", "18"]);
+    }
 
     #[test]
     fn named_view_display_preserves_the_saved_plot_area() {
@@ -119,6 +159,8 @@ pub enum PlotDlgMsg {
     /// the user has since left is ignored.
     PrinterMedia(String, Option<std::sync::Arc<PrinterCapabilities>>),
     Paper(String),
+    /// Edits of the inline "custom paper size" editor under the Size row.
+    CustomPaper(CustomPaperMsg),
     Orientation(String),
     Area(String),
     Scale(String),
@@ -153,6 +195,121 @@ pub enum PlotDlgMsg {
     NameCancel,
 }
 
+/// Which side of the printable-margin row a value belongs to.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum MarginSide {
+    Left,
+    Bottom,
+    Right,
+    Top,
+}
+
+#[derive(Debug, Clone)]
+pub enum CustomPaperMsg {
+    /// Open the editor, seeded from the selected sheet.
+    Open,
+    Cancel,
+    Name(String),
+    Width(String),
+    Height(String),
+    /// Units picked from the dropdown, by their catalogue label.
+    Units(String),
+    Margin(MarginSide, String),
+    /// Add (or replace) the sheet and select it.
+    Add,
+    /// Remove the selected user-defined sheet.
+    Remove,
+}
+
+/// The inline custom-sheet editor's fields, kept as typed text so a half-typed
+/// number does not snap to a value while editing. Everything is in the
+/// draft's own units.
+#[derive(Debug, Clone, PartialEq, Default)]
+pub struct CustomPaperDraft {
+    pub name: String,
+    pub width: String,
+    pub height: String,
+    pub inches: bool,
+    /// Left, bottom, right, top.
+    pub margins: [String; 4],
+    /// Why the last Add was refused, shown under the fields.
+    pub error: Option<CustomPaperError>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CustomPaperError {
+    /// Width or height is not a positive number.
+    Size,
+}
+
+impl CustomPaperDraft {
+    fn units(&self) -> PaperUnits {
+        if self.inches {
+            PaperUnits::Inches
+        } else {
+            PaperUnits::Millimeters
+        }
+    }
+
+    /// Seed the editor from a sheet: its dimensions and unit, and the margins
+    /// given (in millimetres) converted into that unit.
+    pub fn from_paper(paper: &PaperSize, margins_mm: Margins) -> Self {
+        let units = paper.units;
+        let fmt = |v: f64| {
+            let v = units.from_mm(v);
+            if (v - v.round()).abs() < 1e-6 {
+                format!("{}", v.round() as i64)
+            } else {
+                format!("{v:.2}")
+            }
+        };
+        let dim = |v: f64| {
+            if (v - v.round()).abs() < 1e-6 {
+                format!("{}", v.round() as i64)
+            } else {
+                format!("{v:.2}")
+            }
+        };
+        Self {
+            name: paper.label.to_string(),
+            width: dim(paper.width),
+            height: dim(paper.height),
+            inches: units == PaperUnits::Inches,
+            margins: [
+                fmt(margins_mm.left),
+                fmt(margins_mm.bottom),
+                fmt(margins_mm.right),
+                fmt(margins_mm.top),
+            ],
+            error: None,
+        }
+    }
+
+    /// The sheet the fields describe, or the reason they do not describe one.
+    pub fn build(&self) -> Result<CustomPaper, CustomPaperError> {
+        let number = |text: &str| text.trim().replace(',', ".").parse::<f64>().ok();
+        let (Some(width), Some(height)) = (number(&self.width), number(&self.height)) else {
+            return Err(CustomPaperError::Size);
+        };
+        if !(width > 0.0) || !(height > 0.0) || !width.is_finite() || !height.is_finite() {
+            return Err(CustomPaperError::Size);
+        }
+        let margin = |text: &str| number(text).filter(|v| v.is_finite() && *v >= 0.0).unwrap_or(0.0);
+        Ok(CustomPaper {
+            name: self.name.trim().to_string(),
+            width,
+            height,
+            units: self.units(),
+            margins: Margins {
+                left: margin(&self.margins[0]),
+                bottom: margin(&self.margins[1]),
+                right: margin(&self.margins[2]),
+                top: margin(&self.margins[3]),
+            },
+        })
+    }
+}
+
 /// Transient state backing the Plot dialog. Seeded from the layout's plot
 /// settings when the dialog opens; consumed on commit.
 // The persisted fields form the "plot" section of the app config
@@ -173,6 +330,12 @@ pub struct PlotDialogState {
     /// while unknown, when the platform cannot ask, or for PDF output.
     #[serde(skip)]
     pub printer_media: Option<std::sync::Arc<PrinterCapabilities>>,
+    /// Sheets the user defined, offered for every device and remembered
+    /// across sessions.
+    pub custom_papers: Vec<CustomPaper>,
+    /// The inline custom-sheet editor while it is open.
+    #[serde(skip)]
+    pub custom_editor: Option<CustomPaperDraft>,
     /// Chosen printer name, or `None` for the system default.
     pub printer: Option<String>,
     /// Output goes to a PDF file instead of a printer.
@@ -238,6 +401,8 @@ impl Default for PlotDialogState {
             printers: Vec::new(),
             default_printer: None,
             printer_media: None,
+            custom_papers: Vec::new(),
+            custom_editor: None,
             printer: None,
             to_file: false,
             paper: paper_catalog::default_paper().canonical.to_string(),
@@ -318,80 +483,19 @@ fn legacy_fit_to_paper_default() -> bool {
 }
 
 fn btn(accent: bool) -> impl Fn(&Theme, button::Status) -> button::Style {
-    move |theme: &Theme, st| {
-        let palette = theme.palette();
-        let pair = match (accent, st) {
-            (true, button::Status::Hovered | button::Status::Pressed) => palette.primary.strong,
-            (false, button::Status::Hovered | button::Status::Pressed) => {
-                palette.background.strong
-            }
-            (true, _) => palette.primary.base,
-            _ => palette.background.weak,
-        };
-        button::Style {
-        background: Some(Background::Color(pair.color)),
-        text_color: pair.text,
-        border: Border {
-            color: palette.background.neutral.color,
-            width: 1.0,
-            radius: 4.0.into(),
-        },
-        shadow: iced::Shadow::default(),
-        snap: false,
-        }
-    }
-}
-
-fn field_style(theme: &Theme, status: text_input::Status) -> text_input::Style {
-    let palette = theme.palette();
-    let border = match status {
-        text_input::Status::Focused { .. } => palette.primary.base.color,
-        _ => palette.background.neutral.color,
-    };
-    text_input::Style {
-        background: Background::Color(palette.background.base.color),
-        border: Border { color: border, width: 1.0, radius: 3.0.into() },
-        icon: palette.background.base.text,
-        placeholder: palette.background.base.text.scale_alpha(0.48),
-        value: palette.background.base.text,
-        selection: palette.primary.base.color.scale_alpha(0.5),
-    }
-}
-
-fn muted_style(theme: &Theme) -> iced::widget::text::Style {
-    iced::widget::text::Style {
-        color: Some(theme.palette().background.base.text.scale_alpha(0.68)),
-    }
+    form::button_style(accent)
 }
 
 fn hdivider<'a>(width: Length) -> Element<'a, Message> {
-    container(Space::new().width(width).height(1))
-        .width(width)
-        .height(1)
-        .style(|theme: &Theme| container::Style {
-            background: Some(Background::Color(
-                theme.palette().background.neutral.color
-            )),
-            ..Default::default()
-        })
-        .into()
+    form::hdivider(width)
 }
 
 fn section_label<'a>(s: Cow<'static, str>) -> Element<'a, Message> {
-    text(s).size(11).style(muted_style).into()
+    form::section_label(s)
 }
 
 fn vsep<'a>(height: Length) -> Element<'a, Message> {
-    container(Space::new().width(1).height(height))
-        .width(1)
-        .height(height)
-        .style(|theme: &Theme| container::Style {
-            background: Some(Background::Color(
-                theme.palette().background.neutral.color
-            )),
-            ..Default::default()
-        })
-        .into()
+    form::vseparator(height)
 }
 
 fn setup_row<'a>(
@@ -404,7 +508,7 @@ fn setup_row<'a>(
         return text_input("", rename_buf)
             .on_input(|value| Message::PlotDlg(PlotDlgMsg::NameInput(value)))
             .on_submit(Message::PlotDlg(PlotDlgMsg::NameCommit))
-            .style(field_style)
+            .style(form::field_style)
             .size(11)
             .padding([4, 8])
             .width(Fit)
@@ -442,15 +546,7 @@ fn drop_row<'a>(
     ctor: fn(String) -> PlotDlgMsg,
     width: Length,
 ) -> Element<'a, Message> {
-    let pl = iced::widget::pick_list(selected, options, |value| value.to_string())
-        .on_select(move |choice| Message::PlotDlg(ctor(choice.raw)))
-        .text_size(12)
-        .padding([3, 6])
-        .width(width);
-    row![text(label).size(11).style(muted_style).width(92), pl]
-        .spacing(8)
-        .align_y(iced::Center)
-    .into()
+    form::labeled_pick_list(label, options, selected, move |choice| Message::PlotDlg(ctor(choice.raw)), width)
 }
 
 fn drop_row_enabled<'a>(
@@ -461,20 +557,14 @@ fn drop_row_enabled<'a>(
     width: Length,
     enabled: bool,
 ) -> Element<'a, Message> {
-    if enabled {
-        return drop_row(label, options, selected, ctor, width);
-    }
-    row![
-        text(label).size(11).style(muted_style).width(92),
-        crate::ui::read_only::field(
-            selected.map(|choice| choice.to_string()).unwrap_or_default().as_str(),
-            12.0,
-            width,
-        ),
-    ]
-    .spacing(8)
-    .align_y(iced::Center)
-    .into()
+    form::labeled_pick_list_enabled(
+        label,
+        options,
+        selected,
+        move |choice| Message::PlotDlg(ctor(choice.raw)),
+        width,
+        enabled,
+    )
 }
 
 /// A `label : text field` row.
@@ -484,17 +574,7 @@ fn field_row<'a>(
     ctor: fn(String) -> PlotDlgMsg,
     width: u16,
 ) -> Element<'a, Message> {
-    row![
-        text(label).size(11).style(muted_style).width(92),
-        text_input("", value)
-            .on_input(move |s| Message::PlotDlg(ctor(s)))
-            .style(field_style)
-            .size(12)
-            .width(width as f32),
-    ]
-    .spacing(8)
-    .align_y(iced::Center)
-    .into()
+    form::labeled_field(label, value, move |s| Message::PlotDlg(ctor(s)), width as f32)
 }
 
 fn field_row_enabled<'a>(
@@ -504,19 +584,9 @@ fn field_row_enabled<'a>(
     width: u16,
     enabled: bool,
 ) -> Element<'a, Message> {
-    if enabled {
-        return field_row(label, value, ctor, width);
-    }
-    row![
-        text(label).size(11).style(muted_style).width(92),
-        crate::ui::read_only::field(value, 12.0, Length::Fixed(width as f32)),
-    ]
-    .spacing(8)
-    .align_y(iced::Center)
-    .into()
+    form::labeled_field_enabled(label, value, move |s| Message::PlotDlg(ctor(s)), width as f32, enabled)
 }
 
-/// A single option checkbox bound to a `PlotFlag`.
 fn check<'a>(label: Cow<'static, str>, on: bool, flag: PlotFlag) -> Element<'a, Message> {
     checkbox(on)
         .label(label)
@@ -553,6 +623,92 @@ fn choices(items: &[&str]) -> Vec<PlotChoice> {
     items.iter().map(|&value| PlotChoice::localized(value)).collect()
 }
 
+/// The inline editor for a user-defined sheet: name, dimensions and unit,
+/// printable margins, Add / Cancel. Numbers stay text until Add validates
+/// them.
+fn custom_paper_editor<'a>(draft: &'a CustomPaperDraft, width: Length) -> Element<'a, Message> {
+    let msg = |m: CustomPaperMsg| Message::PlotDlg(PlotDlgMsg::CustomPaper(m));
+    let units_label = |inches: bool| {
+        if inches {
+            crate::i18n::translate("Inches")
+        } else {
+            crate::i18n::translate("Millimeters")
+        }
+    };
+    let unit_options: Vec<PlotChoice> = vec![
+        PlotChoice::localized("Millimeters"),
+        PlotChoice::localized("Inches"),
+    ];
+    let unit_selected = Some(PlotChoice::localized(if draft.inches { "Inches" } else { "Millimeters" }));
+    let margin_field = |side: MarginSide, index: usize, hint: &'a str| {
+        form::compact_field(hint, &draft.margins[index], move |v| msg(CustomPaperMsg::Margin(side, v)), 56.0)
+    };
+    let error: Element<'_, Message> = match draft.error {
+        Some(CustomPaperError::Size) => text(t!("Enter a positive width and height."))
+            .size(10)
+            .style(|theme: &Theme| iced::widget::text::Style {
+                color: Some(theme.palette().danger.base.color),
+            })
+            .into(),
+        None => Space::new().height(0).into(),
+    };
+    let unit_hint = text(units_label(draft.inches)).size(10).style(muted_style);
+    container(
+        column![
+            section_label(t!("Custom paper size")),
+            form::labeled_field(t!("Name"), &draft.name, move |v| msg(CustomPaperMsg::Name(v)), 220.0),
+            row![
+                form::labeled_field(t!("Width"), &draft.width, move |v| msg(CustomPaperMsg::Width(v)), 70.0),
+                form::labeled_field(t!("Height"), &draft.height, move |v| msg(CustomPaperMsg::Height(v)), 70.0),
+            ]
+            .spacing(12),
+            form::labeled_pick_list(
+                t!("Units"),
+                unit_options,
+                unit_selected,
+                move |choice| msg(CustomPaperMsg::Units(choice.raw)),
+                Length::Fixed(140.0),
+            ),
+            row![
+                text(t!("Printable margins")).size(11).style(muted_style).width(form::LABEL_WIDTH),
+                margin_field(MarginSide::Left, 0, "L"),
+                margin_field(MarginSide::Bottom, 1, "B"),
+                margin_field(MarginSide::Right, 2, "R"),
+                margin_field(MarginSide::Top, 3, "T"),
+                unit_hint,
+            ]
+            .spacing(6)
+            .align_y(iced::Center),
+            error,
+            row![
+                Space::new().width(Length::Fill),
+                button(text(t!("Cancel")).size(11))
+                    .on_press(msg(CustomPaperMsg::Cancel))
+                    .style(btn(false))
+                    .padding([4, 10]),
+                button(text(t!("Add")).size(11))
+                    .on_press(msg(CustomPaperMsg::Add))
+                    .style(btn(true))
+                    .padding([4, 12]),
+            ]
+            .spacing(6),
+        ]
+        .spacing(6),
+    )
+    .padding(8)
+    .width(width)
+    .style(|theme: &Theme| container::Style {
+        background: Some(Background::Color(theme.palette().background.weak.color)),
+        border: Border {
+            color: theme.palette().background.neutral.color,
+            width: 1.0,
+            radius: 4.0.into(),
+        },
+        ..Default::default()
+    })
+    .into()
+}
+
 pub fn view_window(
     s: &PlotDialogState,
     print_all_options: bool,
@@ -599,7 +755,7 @@ pub fn view_window(
                 text_input("", rename_buf)
                     .on_input(|value| Message::PlotDlg(PlotDlgMsg::NameInput(value)))
                     .on_submit(Message::PlotDlg(PlotDlgMsg::NameCommit))
-                    .style(field_style)
+                    .style(form::field_style)
                     .size(11)
                     .padding([4, 8])
                     .width(Length::Fill),
@@ -708,10 +864,21 @@ pub fn view_window(
         Some(caps) => caps.media.iter().map(|media| PlotChoice::paper(&media.paper)).collect(),
         None => paper_catalog::catalog().iter().map(PlotChoice::paper).collect(),
     };
+    // User-defined sheets come last, after whatever the device offers.
+    for custom in &s.custom_papers {
+        let choice = PlotChoice::paper(&custom.paper());
+        if !paper_opts.contains(&choice) {
+            paper_opts.push(choice);
+        }
+    }
     let paper_sel = PlotChoice::paper(&selected_paper);
     if !paper_opts.contains(&paper_sel) {
         paper_opts.insert(0, paper_sel.clone());
     }
+    let selected_is_custom = s
+        .custom_papers
+        .iter()
+        .any(|custom| custom.canonical() == selected_paper.canonical);
     let paper_source_note: Element<'_, Message> = if printer_sheets.is_some() {
         text(t!("Sheet sizes and printable areas reported by the printer."))
             .size(10)
@@ -768,9 +935,36 @@ pub fn view_window(
     );
 
     // ── Paper, area, offset, scale ────────────────────────────────────────
+    // Size row with the custom-sheet controls; the editor unfolds below it.
+    let mut size_row = row![
+        drop_row(t!("Size"), paper_opts, Some(paper_sel), PlotDlgMsg::Paper, Length::Fill),
+    ]
+    .spacing(6)
+    .align_y(iced::Center);
+    if s.custom_editor.is_none() {
+        size_row = size_row.push(
+            button(text(t!("Custom…")).size(11))
+                .on_press(Message::PlotDlg(PlotDlgMsg::CustomPaper(CustomPaperMsg::Open)))
+                .style(btn(false))
+                .padding([4, 8]),
+        );
+        if selected_is_custom {
+            size_row = size_row.push(
+                button(text(t!("Remove")).size(11))
+                    .on_press(Message::PlotDlg(PlotDlgMsg::CustomPaper(CustomPaperMsg::Remove)))
+                    .style(btn(false))
+                    .padding([4, 8]),
+            );
+        }
+    }
+    let custom_editor: Element<'_, Message> = match &s.custom_editor {
+        Some(draft) => custom_paper_editor(draft, width),
+        None => Space::new().height(0).into(),
+    };
     let paper_panel = panel(column![
         section_label(t!("Paper")),
-        drop_row(t!("Size"), paper_opts, Some(paper_sel), PlotDlgMsg::Paper, width),
+        size_row,
+        custom_editor,
         paper_source_note,
         paper_note,
     ].spacing(7));