diff --git a/crates/ui-egui/src/panels/format_shape.rs b/crates/ui-egui/src/panels/format_shape.rs
--- a/crates/ui-egui/src/panels/format_shape.rs
+++ b/crates/ui-egui/src/panels/format_shape.rs
@@ -147,9 +147,16 @@ pub(super) fn format_shape(app: &mut SlideApp, ui: &mut Ui) {
             }
         }
         "size" => {
-            let lock_id = egui::Id::unique("fmt-lock-aspect");
+            let lock_id = ui.scope_id().with("fmt-lock-aspect");
             let mut lock: bool = ui.data_mut(|d| d.get_temp(lock_id).unwrap_or(false));
             let locked = lock;
+            // Scale is measured from the size the shape had when this tab first showed it, like the
+            // Size and Position dialog; the origin choice is kept for the session.
+            let base_id = ui.scope_id().with(("fmt-scale-base", uid, sh.id.0));
+            let (base_w, base_h): (f64, f64) = ui.data_mut(|d| d.get_temp(base_id).unwrap_or((x.w, x.h)));
+            ui.data_mut(|d| d.insert_temp(base_id, (base_w, base_h)));
+            let origin_id = ui.scope_id().with("fmt-origin-center");
+            let mut center: bool = ui.data_mut(|d| d.get_temp(origin_id).unwrap_or(false));
             let len = app.session.prefs.units;
             let mut fields = |ui: &mut Ui, label: &str, id: &str, v: f64, key: &str, cmd: &str, angle: bool| {
                 let (unit, suffix) = if angle { (1.0, "°") } else { (len.points_per_unit(), len.suffix()) };
@@ -168,13 +175,50 @@ pub(super) fn format_shape(app: &mut SlideApp, ui: &mut Ui) {
             fields(ui, "Height", "fh", x.h, "h", "shape.resize", false);
             fields(ui, "Width", "fw", x.w, "w", "shape.resize", false);
             fields(ui, "Rotation", "fr", x.rot, "deg", "shape.rotate", true);
+            for (label, id, cur, base, key) in [("Scale Height", "fsh", x.h, base_h, "h"), ("Scale Width", "fsw", x.w, base_w, "w")] {
+                ui.horizontal(|ui| {
+                    ui.add_sized(vec2(90.0, 20.0), egui::Label::new(label));
+                    let pct = if base > 0.0 { cur / base * 100.0 } else { 100.0 };
+                    if let Some(nv) = widgets::spinner(ui, id, label, pct, 1.0, "%", 70.0)
+                        && nv > 0.0
+                    {
+                        let mut p = json!({key: base * nv / 100.0});
+                        if locked {
+                            p["lockAspect"] = json!(true);
+                        }
+                        run(app, "shape.sizePosition", p);
+                    }
+                });
+            }
             if ui.checkbox(&mut lock, "Lock aspect ratio").changed() {
                 ui.data_mut(|d| d.insert_temp(lock_id, lock));
             }
             ui.add_space(6.0);
             ui.label(egui::RichText::new("Position").font(theme::bold(13.0)));
-            fields(ui, "Horizontal", "fx", x.x, "x", "shape.move", false);
-            fields(ui, "Vertical", "fy", x.y, "y", "shape.move", false);
+            ui.horizontal(|ui| {
+                ui.add_sized(vec2(90.0, 20.0), egui::Label::new("From"));
+                let combo =
+                    egui::ComboBox::from_id_salt("fmt-origin").selected_text(if center { "Center" } else { "Top Left Corner" }).show_ui(ui, |ui| {
+                        ui.selectable_value(&mut center, false, "Top Left Corner");
+                        ui.selectable_value(&mut center, true, "Center");
+                    });
+                combo.response.widget_info(|| egui::WidgetInfo::labeled(egui::Role::ComboBox, true, "From"));
+            });
+            ui.data_mut(|d| d.insert_temp(origin_id, center));
+            let (dx, dy) = if center { (x.w / 2.0, x.h / 2.0) } else { (0.0, 0.0) };
+            // The spinner shows `value / unit`; `shape.move` takes the top-left corner, so a centre
+            // reading is shifted by half the size in both directions.
+            let (px, py) = (x.x + dx, x.y + dy);
+            let mut pos = |ui: &mut Ui, label: &str, id: &str, v: f64, off: f64, key: &str| {
+                ui.horizontal(|ui| {
+                    ui.add_sized(vec2(90.0, 20.0), egui::Label::new(label));
+                    if let Some(nv) = widgets::spinner(ui, id, label, v / len.points_per_unit(), 0.1, len.suffix(), 70.0) {
+                        run(app, "shape.move", json!({key: nv * len.points_per_unit() - off}));
+                    }
+                });
+            };
+            pos(ui, "Horizontal", "fx", px, dx, "x");
+            pos(ui, "Vertical", "fy", py, dy, "y");
             ui.add_space(6.0);
             ui.label(egui::RichText::new("Alt Text").font(theme::bold(13.0)));
             let id = ui.scope_id().with(("alt", uid, sh.id.0));
diff --git a/crates/ui-egui/src/units_tests.rs b/crates/ui-egui/src/units_tests.rs
--- a/crates/ui-egui/src/units_tests.rs
+++ b/crates/ui-egui/src/units_tests.rs
@@ -211,3 +211,41 @@ fn the_ruler_counts_centimetres_in_halves_and_inches_in_quarters() {
     // A hand-edited prefs.json can say points: the ruler stays in inches rather than a tick per point.
     assert_eq!(crate::canvas::ruler_steps(Unit::Points), (72.0, 4));
 }
+
+fn type_into(h: &mut Harness<'_, SlideApp>, shown: &str, text: &str) {
+    h.query_all_by_role(Role::TextInput).rfind(|n| n.value().as_deref() == Some(shown)).unwrap().focus();
+    h.run_steps(1);
+    h.key_press_modifiers(egui::Modifiers::COMMAND, egui::Key::A);
+    h.query_all_by_role(Role::TextInput).find(|n| n.is_focused()).unwrap().type_text(text);
+    h.run_steps(1);
+    h.key_press(egui::Key::Enter);
+    h.run_steps(3);
+}
+
+/// Format Shape › Size & Properties: Scale Width/Height and the From origin of Position.
+#[test]
+fn the_format_pane_scales_and_positions_from_the_centre() {
+    let mut app = app_with_shape(Unit::default());
+    app.ui.pane = Some("format".into());
+    app.ui.format_tab = "size".into();
+    let mut h = harness(app);
+    h.run_steps(3);
+    let shown = text_values(&h);
+    assert_eq!(shown.iter().filter(|s| *s == "100%").count(), 2, "{shown:?}");
+    // 50% Scale Width (the last "100%" row) halves the 144 pt width.
+    type_into(&mut h, "100%", "50");
+    let x = selected_xfrm(h.state());
+    assert!((x.w - 72.0).abs() < 1e-6 && (x.h - 108.0).abs() < 1e-6, "{x:?}");
+    assert!(text_values(&h).iter().any(|s| s == "50%"));
+    // From Center: the fields read the middle of the box, and typing moves the middle.
+    h.get_by_role_and_label(Role::ComboBox, "From").click();
+    h.run_steps(2);
+    h.get_by_label("Center").click();
+    h.run_steps(3);
+    // Box is now (72, 36, 72, 108): its centre is (108, 90) pt = (1.5", 1.25").
+    let shown = text_values(&h);
+    assert!(shown.iter().any(|s| s == "1.5\"") && shown.iter().any(|s| s == "1.25\""), "{shown:?}");
+    type_into(&mut h, "1.5\"", "3");
+    let x = selected_xfrm(h.state());
+    assert!((x.x - 180.0).abs() < 1e-6 && (x.w - 72.0).abs() < 1e-6 && (x.y - 36.0).abs() < 1e-6, "{x:?}");
+}