diff --git a/crates/tools/src/shape.rs b/crates/tools/src/shape.rs
index 07593a72b..2ac761417 100644
--- a/crates/tools/src/shape.rs
+++ b/crates/tools/src/shape.rs
@@ -201,7 +201,9 @@ impl Tool for ShapeTool {
                     self.began = false;
                     vec![Action::Commit]
                 } else {
-                    vec![Action::Dialog(self.id.into(), json!({ "x": s.x, "y": s.y }))]
+                    // Alt (draw from centre) is passed on, so the size dialog can centre the shape on the click.
+                    let args = if ev.mods.alt { json!({ "x": s.x, "y": s.y, "alt": true }) } else { json!({ "x": s.x, "y": s.y }) };
+                    vec![Action::Dialog(self.id.into(), args)]
                 }
             }
             _ => vec![],
@@ -385,6 +387,21 @@ mod tests {
         );
     }
 
+    #[test]
+    fn alt_click_passes_draw_from_centre_to_the_dialog() {
+        let (d, _) = doc_with_rect();
+        let s = Selection::default();
+        let p = paint();
+        let cx = cx(&d, &s, &p);
+        let alt = Mods { alt: true, ..Default::default() };
+        let mut t = ShapeTool::new("rectangle");
+        t.pointer(&cx, &PointerEvent::new(PointerKind::Down, 10.0, 10.0).with_mods(alt));
+        assert_eq!(
+            t.pointer(&cx, &PointerEvent::new(PointerKind::Up, 10.0, 10.0).with_mods(alt)),
+            vec![Action::Dialog("rectangle".into(), json!({"x": 10.0, "y": 10.0, "alt": true}))]
+        );
+    }
+
     #[test]
     fn arrow_keys_change_sides() {
         let (d, _) = doc_with_rect();
diff --git a/crates/ui-egui/src/dialogs/shapes.rs b/crates/ui-egui/src/dialogs/shapes.rs
index c8e2dd535..b0a3a1fd0 100644
--- a/crates/ui-egui/src/dialogs/shapes.rs
+++ b/crates/ui-egui/src/dialogs/shapes.rs
@@ -93,6 +93,16 @@ fn body(app: &mut VectorcraftApp, ui: &mut egui::Ui, d: &mut Dialog) -> bool {
     false
 }
 
+/// The top-left corner of a rectangle or ellipse: the click itself, or with Alt held (draw from centre) the click minus half the size.
+fn box_origin(d: &Dialog) -> (f64, f64) {
+    let (x, y) = (d.f64("x", 0.0), d.f64("y", 0.0));
+    if d.fields.get("alt").and_then(Value::as_bool).unwrap_or(false) {
+        (x - d.f64("width", 100.0) / 2.0, y - d.f64("height", 100.0) / 2.0)
+    } else {
+        (x, y)
+    }
+}
+
 fn confirm(app: &mut VectorcraftApp, d: &Dialog) -> Result<Value, String> {
     let count = match d.kind.as_str() {
         "polygon" => Some(("sides", 6.0, 3.0)),
@@ -105,8 +115,9 @@ fn confirm(app: &mut VectorcraftApp, d: &Dialog) -> Result<Value, String> {
         values
     });
     let (x, y) = (d.f64("x", 0.0), d.f64("y", 0.0));
+    let (bx, by) = box_origin(d);
     let (id, params) = match d.kind.as_str() {
-        "ellipse" => ("shape.ellipse", json!({"x": x, "y": y, "width": d.f64("width", 100.0), "height": d.f64("height", 100.0)})),
+        "ellipse" => ("shape.ellipse", json!({"x": bx, "y": by, "width": d.f64("width", 100.0), "height": d.f64("height", 100.0)})),
         "polygon" => ("shape.polygon", json!({"cx": x, "cy": y, "radius": d.f64("radius", 50.0), "sides": d.f64("sides", 6.0) as u64})),
         "star" => (
             "shape.star",
@@ -131,7 +142,7 @@ fn confirm(app: &mut VectorcraftApp, d: &Dialog) -> Result<Value, String> {
         }
         _ => (
             "shape.rectangle",
-            json!({"x": x, "y": y, "width": d.f64("width", 100.0), "height": d.f64("height", 100.0), "radius": d.f64("radius", 0.0)}),
+            json!({"x": bx, "y": by, "width": d.f64("width", 100.0), "height": d.f64("height", 100.0), "radius": d.f64("radius", 0.0)}),
         ),
     };
     // On the active plane while the perspective grid shows, sized in plane units from the click.
@@ -145,3 +156,15 @@ fn confirm(app: &mut VectorcraftApp, d: &Dialog) -> Result<Value, String> {
     }
     Ok(result)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn alt_click_centres_the_typed_size_on_the_click() {
+        let fields = |alt: bool| Dialog::new("rectangle", json!({"x": 100.0, "y": 50.0, "alt": alt, "width": "40 pt", "height": "20 pt"}));
+        assert_eq!(box_origin(&fields(false)), (100.0, 50.0));
+        assert_eq!(box_origin(&fields(true)), (80.0, 40.0));
+    }
+}
diff --git a/crates/ui-egui/src/dialogs/tools.rs b/crates/ui-egui/src/dialogs/tools.rs
index 9087cc80d..1947742ac 100644
--- a/crates/ui-egui/src/dialogs/tools.rs
+++ b/crates/ui-egui/src/dialogs/tools.rs
@@ -11,9 +11,10 @@ use crate::state::Dialog;
 pub fn open_tool_dialog(app: &mut VectorcraftApp, kind: &str, p: Value) {
     let x = p.get("x").and_then(Value::as_f64).unwrap_or(0.0);
     let y = p.get("y").and_then(Value::as_f64).unwrap_or(0.0);
+    let alt = p.get("alt").and_then(Value::as_bool).unwrap_or(false);
     let d = match kind {
-        "rectangle" | "ellipse" => Dialog::new(kind, json!({"x": x, "y": y, "width": "100 pt", "height": "100 pt"})),
-        "roundedRectangle" => Dialog::new(kind, json!({"x": x, "y": y, "width": "100 pt", "height": "100 pt", "radius": "12 pt"})),
+        "rectangle" | "ellipse" => Dialog::new(kind, json!({"x": x, "y": y, "alt": alt, "width": "100 pt", "height": "100 pt"})),
+        "roundedRectangle" => Dialog::new(kind, json!({"x": x, "y": y, "alt": alt, "width": "100 pt", "height": "100 pt", "radius": "12 pt"})),
         "polygon" => Dialog::new(kind, json!({"x": x, "y": y, "radius": "50 pt", "sides": app.session.tool_options_of(kind)["sides"]})),
         "star" => {
             Dialog::new(kind, json!({"x": x, "y": y, "radius1": "50 pt", "radius2": "25 pt", "points": app.session.tool_options_of(kind)["points"]}))