diff --git a/crates/engine/src/cmd/format.rs b/crates/engine/src/cmd/format.rs
index 4f13bf9c6..2b6e50b7f 100644
--- a/crates/engine/src/cmd/format.rs
+++ b/crates/engine/src/cmd/format.rs
@@ -156,7 +156,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Row Height…",
             ["Home", "Cells", "Format"],
             None,
-            "{rows?: \"2:5\", height: 20 (points on screen)}",
+            "{rows?: \"2:5\" | \"2:2,4:5\", height: 20 (points on screen)}",
             has_doc,
             row_height
         ),
@@ -165,7 +165,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Column Width…",
             ["Home", "Cells", "Format"],
             None,
-            "{cols?: \"B:D\", width: 64 (points) | chars: 8.43}",
+            "{cols?: \"B:D\" | \"B:B,D:F\", width: 64 (points) | chars: 8.43}",
             has_doc,
             col_width
         ),
@@ -910,8 +910,14 @@ fn cell_style(s: &mut Session, p: &Json) -> Result<Json> {
 fn line_targets(s: &Session, p: &Json, rows: bool) -> Result<Vec<(u32, u32)>> {
     let key = if rows { "rows" } else { "cols" };
     if let Some(t) = str_param(p, key) {
-        let r = RangeRef::parse(t).ok_or_else(|| bad(key, format!("not a range: {t}")))?;
-        return Ok(vec![if rows { (r.start.row, r.end.row) } else { (r.start.col, r.end.col) }]);
+        // A comma-separated list ("B:B,D:F") targets several areas, like a multi-area selection.
+        return t
+            .split(',')
+            .map(|part| {
+                let r = RangeRef::parse(part).ok_or_else(|| bad(key, format!("not a range: {part}")))?;
+                Ok(if rows { (r.start.row, r.end.row) } else { (r.start.col, r.end.col) })
+            })
+            .collect();
     }
     Ok(s.doc()?.selection.ranges.iter().map(|r| if rows { (r.start.row, r.end.row) } else { (r.start.col, r.end.col) }).collect())
 }
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 6bd03d55e..3c08ee085 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -1633,3 +1633,27 @@ fn notes_comments_and_links_survive_a_json_save() {
     assert_eq!(after.hyperlinks, before.hyperlinks);
     assert_eq!(after.cells, before.cells);
 }
+
+#[test]
+fn row_height_and_column_width_take_a_list_of_areas() {
+    // Issue #341: header drags on a multi-area selection size every selected line in one step.
+    let mut s = s();
+    s.execute("home.columnWidth", json!({"cols": "B:B,D:E", "width": 120})).unwrap();
+    s.execute("home.rowHeight", json!({"rows": "2:2,4:5", "height": 40})).unwrap();
+    let widths: Vec<f32> = (0..6).map(|c| s.doc().unwrap().wb.active().unwrap().col_width(c)).collect();
+    let heights: Vec<f32> = (0..6).map(|r| s.doc().unwrap().wb.active().unwrap().row_height(r)).collect();
+    for c in [1, 3, 4] {
+        assert_eq!(widths[c], 120.0, "column {c}");
+    }
+    for c in [0, 2, 5] {
+        assert_ne!(widths[c], 120.0, "column {c}");
+    }
+    for r in [1, 3, 4] {
+        assert_eq!(heights[r], 40.0, "row {r}");
+    }
+    for r in [0, 2, 5] {
+        assert_ne!(heights[r], 40.0, "row {r}");
+    }
+    assert!(s.execute("home.columnWidth", json!({"cols": "B:B,nope", "width": 50})).is_err());
+    assert_eq!(s.doc().unwrap().wb.active().unwrap().col_width(1), 120.0, "a bad list changes nothing");
+}
diff --git a/crates/ui-egui/src/grid.rs b/crates/ui-egui/src/grid.rs
index 72d33e2dc..d228e515d 100644
--- a/crates/ui-egui/src/grid.rs
+++ b/crates/ui-egui/src/grid.rs
@@ -1359,8 +1359,10 @@ fn interact(app: &mut SheetApp, ui: &mut egui::Ui, resp: &egui::Response, geo: &
                 let w = (orig + (p.x - start) / geo.z).max(0.0);
                 app.toast =
                     Some((format!("Width: {:.2} ({} pixels)", gridcraft_engine::cmd::format::points_to_chars(w as f64), w.round()), crate::now_ms()));
+                // Inside a selection of whole columns, every selected column takes the new width
+                // (Ctrl-selected areas included); otherwise only the dragged one.
                 let cols = if sel.ranges.iter().any(|r| r.is_full_cols() && col >= r.start.col && col <= r.end.col) {
-                    sel.current().a1()
+                    sel.ranges.iter().filter(|r| r.is_full_cols()).map(|r| r.a1()).collect::<Vec<_>>().join(",")
                 } else {
                     RangeRef::cols(col, col).a1()
                 };
@@ -1371,7 +1373,12 @@ fn interact(app: &mut SheetApp, ui: &mut egui::Ui, resp: &egui::Response, geo: &
                 let h = (orig + (p.y - start) / geo.z).max(0.0);
                 app.toast = Some((format!("Height: {:.2} ({} pixels)", h * 0.75, h.round()), crate::now_ms()));
                 let rows = if sel.ranges.iter().any(|r| r.is_full_rows() && row >= r.start.row && row <= r.end.row) {
-                    format!("{}:{}", sel.current().start.row + 1, sel.current().end.row + 1)
+                    sel.ranges
+                        .iter()
+                        .filter(|r| r.is_full_rows())
+                        .map(|r| format!("{}:{}", r.start.row + 1, r.end.row + 1))
+                        .collect::<Vec<_>>()
+                        .join(",")
                 } else {
                     format!("{}:{}", row + 1, row + 1)
                 };
diff --git a/crates/ui-egui/tests/header_autofit.rs b/crates/ui-egui/tests/header_autofit.rs
index 8a6673855..7d1bbbc0f 100644
--- a/crates/ui-egui/tests/header_autofit.rs
+++ b/crates/ui-egui/tests/header_autofit.rs
@@ -114,3 +114,41 @@ fn dragging_a_header_boundary_still_resizes_normally() {
         assert!(!h.state().session.journal.iter().any(|(id, _)| id.starts_with("home.autofit")));
     }
 }
+
+#[test]
+fn dragging_a_boundary_inside_a_multi_area_selection_resizes_every_selected_line() {
+    // Issue #341: Ctrl-selected rows/columns resize together; unselected lines keep their size.
+    for (rows, selection, dragged, changed) in [
+        (false, "A:A,C:C", 2, [true, false, true, false]),
+        (false, "A:A,C:C", 0, [true, false, true, false]),
+        (false, "A:A,C:D", 3, [true, false, true, true]),
+        (false, "A:A,C:C", 1, [false, true, false, false]),
+        (false, "A:A,C3", 0, [true, false, false, false]),
+        (true, "1:1,3:3", 2, [true, false, true, false]),
+        (true, "1:1,3:3", 0, [true, false, true, false]),
+        (true, "1:1,3:4", 3, [true, false, true, true]),
+        (true, "1:1,3:3", 1, [false, true, false, false]),
+        (true, "1:1,C3", 0, [true, false, false, false]),
+    ] {
+        let mut h = harness(selection);
+        let before = sizes(&h, rows);
+        let (start, zoom) = edge(&h, rows, dragged);
+        let delta = if rows { vec2(0.0, 30.0) } else { vec2(30.0, 0.0) };
+        button(&mut h, start, true);
+        h.input_mut().events.push(Event::PointerMoved(start + delta / 2.0));
+        h.step();
+        h.input_mut().events.push(Event::PointerMoved(start + delta));
+        h.step();
+        button(&mut h, start + delta, false);
+        h.run_steps(2);
+        let after = sizes(&h, rows);
+        let expected = (before[dragged as usize] + 30.0 / zoom).round();
+        for (index, changed) in changed.iter().enumerate() {
+            let want = if *changed { expected } else { before[index] };
+            assert_eq!(after[index], want, "selection {selection}, dragged {dragged}, line {index}");
+        }
+        assert_eq!(h.state().session.active().unwrap().undo.len(), 1, "selection {selection}: one undo step");
+        h.state_mut().session.execute("edit.undo", json!({})).unwrap();
+        assert_eq!(sizes(&h, rows), before, "selection {selection}: undo restores every line");
+    }
+}