diff --git a/src/wm.c b/src/wm.c
index aa125b6d..2d680cd6 100644
--- a/src/wm.c
+++ b/src/wm.c
@@ -243,6 +243,16 @@ void wm_stack_move_to_top(struct wm *wm, struct win *w) {
 	wm_stack_move_before(wm, w, wm->window_stack.next);
 }
 
+unsigned wm_stack_num_managed_windows(const struct wm *wm) {
+	unsigned count = 0;
+	list_foreach(struct win, w, &wm->window_stack, stack_neighbour) {
+		if (w->managed) {
+			count += 1;
+		}
+	}
+	return count;
+}
+
 struct managed_win *wm_find_by_client(struct wm *wm, xcb_window_t client) {
 	if (!client) {
 		return NULL;
diff --git a/src/wm.h b/src/wm.h
index 7d7a023a..b9778c19 100644
--- a/src/wm.h
+++ b/src/wm.h
@@ -87,6 +87,7 @@ void wm_stack_move_to_top(struct wm *wm, struct win *w);
 /// Replace window `old` with `new_` in the stack, also replace the window in the hash
 /// table. `old` will be freed.
 void wm_stack_replace(struct wm *wm, struct win *old, struct win *new_);
+unsigned attr_const wm_stack_num_managed_windows(const struct wm *wm);
 
 struct subwin *wm_subwin_add_and_subscribe(struct wm *wm, struct x_connection *c,
                                            xcb_window_t id, xcb_window_t parent);