diff --git a/crates/engine/src/cmd/format.rs b/crates/engine/src/cmd/format.rs
index 4712351ca..c7e970fa5 100644
--- a/crates/engine/src/cmd/format.rs
+++ b/crates/engine/src/cmd/format.rs
@@ -1008,7 +1008,7 @@ pub fn chars_to_points(c: f64) -> f64 {
 pub use gridcraft_model::points_to_chars;
 
 /// Approximate text width in points for autofit (no font metrics in the engine: average glyph
-/// widths for the default font; the UI refines with real measurement when it autofits).
+/// widths for the default font; a front end with fonts measures instead, see `Session::text_width`).
 pub fn approx_text_width(text: &str, size: f32, bold: bool) -> f32 {
     let mut w = 0.0;
     for c in text.chars() {
@@ -1027,6 +1027,7 @@ pub fn approx_text_width(text: &str, size: f32, bold: bool) -> f32 {
 
 fn autofit_cols(s: &mut Session, p: &Json) -> Result<Json> {
     let lines = line_targets(s, p, false)?;
+    let measure = s.text_width.clone();
     edit(s, |cx| {
         let si = cx.sheet_index();
         let Some(sh) = cx.wb.sheet(si) else { return Ok(Json::Null) };
@@ -1044,9 +1045,11 @@ fn autofit_cols(s: &mut Session, p: &Json) -> Result<Json> {
                     let st = cx.wb.styles.get(sh.style_id(cell));
                     let text = crate::display::cell_text(&cx.wb, sh, cell);
                     for line in text.lines() {
-                        max = max.max(
-                            approx_text_width(line, st.font.size, st.font.bold) + 6.0 + st.align.indent as f32 * 9.0 + sh.filter_button_space(cell),
-                        );
+                        let w = match &measure {
+                            Some(m) => m(line, &st.font),
+                            None => approx_text_width(line, st.font.size, st.font.bold),
+                        };
+                        max = max.max(w + 6.0 + st.align.indent as f32 * 9.0 + sh.filter_button_space(cell));
                     }
                 }
                 if max > 0.0 {
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index 258a1cb72..daa9875e5 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -227,6 +227,10 @@ pub enum UiRequest {
     OpenUrl(String),
 }
 
+/// Width in points of one line of text drawn in a cell font, measured by a front end that has
+/// the font the grid draws with.
+pub type TextWidth = Arc<dyn Fn(&str, &model::Font) -> f32 + Send + Sync>;
+
 #[derive(Default)]
 pub struct Session {
     docs: Vec<DocState>,
@@ -256,6 +260,9 @@ pub struct Session {
     /// Review › Notes › Show All Notes: every note is displayed. An application display setting
     /// (like Excel's comment indicator option), so it's not saved in the file.
     pub show_all_notes: bool,
+    /// Measures cell text for AutoFit Column Width. Without it (CLI, MCP) AutoFit uses
+    /// [`cmd::format::approx_text_width`].
+    pub text_width: Option<TextWidth>,
 }
 
 impl Session {
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index f96cdac3c..c9616bc0e 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -990,6 +990,10 @@ impl SheetApp {
 
     /// Per-frame logic (control channel, screenshots). Call before `ui`.
     pub fn logic(&mut self, ctx: &egui::Context) {
+        if self.session.text_width.is_none() {
+            let ctx = ctx.clone();
+            self.session.text_width = Some(std::sync::Arc::new(move |text, font| theme::cell_text_width(&ctx, text, font)));
+        }
         // A keytip control request lives one frame: the ribbon consumes it during `ui`, and
         // anything that never reached a control (collapsed ribbon, tab switch) is dropped.
         self.ui.keytip_invoke = None;
diff --git a/crates/ui-egui/src/theme.rs b/crates/ui-egui/src/theme.rs
index 485b9a2f3..23c7fd35e 100644
--- a/crates/ui-egui/src/theme.rs
+++ b/crates/ui-egui/src/theme.rs
@@ -192,6 +192,17 @@ pub fn cell_family(name: &str, bold: bool, italic: bool) -> FontFamily {
     )
 }
 
+/// Width in points, at 100% zoom, of one line of cell text drawn as the grid draws it: in the
+/// face [`cell_family`] picks, which on a machine without the named font is a wider or narrower
+/// substitute (#1316). A family the active font set doesn't have yet (bound fonts apply from the
+/// next frame) falls back to the engine's estimate rather than letting egui panic on it.
+pub fn cell_text_width(ctx: &egui::Context, text: &str, font: &gridcraft_engine::model::Font) -> f32 {
+    let family = cell_family(&font.name, font.bold, font.italic);
+    let id = FontId::new(font.size * 96.0 / 72.0, family);
+    ctx.fonts_mut(|f| f.families().contains(&id.family).then(|| f.layout_no_wrap(text.to_owned(), id, Color32::PLACEHOLDER).size().x))
+        .unwrap_or_else(|| gridcraft_engine::cmd::format::approx_text_width(text, font.size, font.bold))
+}
+
 /// Whether epaint can open face `index` of this font file and it maps characters to glyphs.
 /// epaint panics (in `Context::set_fonts`, i.e. on startup) on a face it can't open, so every font
 /// file we did not ship is checked first with the same parser and the same call epaint makes
diff --git a/crates/ui-egui/tests/header_autofit.rs b/crates/ui-egui/tests/header_autofit.rs
index 5e123809f..b4f104f4b 100644
--- a/crates/ui-egui/tests/header_autofit.rs
+++ b/crates/ui-egui/tests/header_autofit.rs
@@ -191,3 +191,30 @@ fn table_filter_autofit_works_through_command_and_header_double_click() {
         }
     }
 }
+
+#[test]
+fn header_double_click_fits_the_text_as_the_grid_draws_it() {
+    // Issue #1316: `@` and `%` are far wider in every real font than the engine's average-glyph
+    // estimate, so AutoFit has to measure with the font the grid draws the cell in.
+    let text = "sarmstrong@example.com %%% @@@";
+    let mut h = harness("A1");
+    h.state_mut().session.execute("range.setValues", json!({"range":"A1", "values":[[text]]})).unwrap();
+    h.run_steps(3);
+    let (pos, _) = edge(&h, false, 0);
+    button(&mut h, pos, true);
+    button(&mut h, pos, false);
+    h.step();
+    button(&mut h, pos, true);
+    button(&mut h, pos, false);
+    h.run_steps(2);
+
+    let app = h.state();
+    let sheet = app.session.active().unwrap().wb.active().unwrap();
+    let font = &app.session.active().unwrap().wb.styles.get(sheet.style_id(gridcraft_engine::core::CellRef::new(0, 0))).font;
+    let id = egui::FontId::new(font.size * 96.0 / 72.0, gridcraft_ui_egui::theme::cell_family(&font.name, font.bold, font.italic));
+    let drawn = h.ctx.fonts_mut(|f| f.layout_no_wrap(text.to_string(), id, egui::Color32::BLACK)).size().x;
+    let estimate = gridcraft_engine::cmd::format::approx_text_width(text, font.size, font.bold);
+    assert!(drawn > estimate + 6.0, "fixture: the drawn text ({drawn}) must be wider than the estimate ({estimate}) plus padding");
+    // Two 2.5 px paddings and the gridline, as the grid lays out the cell.
+    assert!(sheet.col_width(0) >= drawn + 6.0, "column {} is narrower than the drawn text {drawn} + padding", sheet.col_width(0));
+}