diff --git a/src/spectrogram.c b/src/spectrogram.c
index 527b57e..4d94062 100644
--- a/src/spectrogram.c
+++ b/src/spectrogram.c
@@ -62,6 +62,43 @@ static float ScopeDivider(void)
     return app.showScope ? app.dividerY : 1.0f;
 }
 
+// Screen layout metrics, derived from window size + UI scale. Single source of
+// truth: the input, selection, and render passes all unpack from this so the
+// layout formulas live in exactly one place.
+typedef struct {
+    float scale;
+    float sidebarWidth;
+    float labelHeight;
+    float scrollbarHeight;
+    float freqLabelWidth;
+    float vScrollbarWidth;
+    float topMargin;
+    float bottomMargin;
+    float spectroHeight;   // height of the spectrogram (respects the scope divider)
+    Rectangle viewBounds;  // the spectrogram drawing area
+} Layout;
+
+static Layout ComputeLayout(void)
+{
+    Layout L;
+    L.scale = GetUIScale();
+    L.sidebarWidth = 320 * L.scale;
+    L.labelHeight = 15 * L.scale;
+    L.scrollbarHeight = 18 * L.scale;
+    L.freqLabelWidth = 65 * L.scale;
+    L.vScrollbarWidth = 18 * L.scale;
+    L.topMargin = 50 * L.scale;
+    L.bottomMargin = 10 * L.scale;
+    L.spectroHeight = (GetScreenHeight() - L.topMargin - L.bottomMargin - L.labelHeight - L.scrollbarHeight - 10 * L.scale) * ScopeDivider();
+    L.viewBounds = (Rectangle){
+        L.sidebarWidth + L.freqLabelWidth,
+        L.topMargin,
+        GetScreenWidth() - L.sidebarWidth - L.freqLabelWidth - L.vScrollbarWidth - 20 * L.scale,
+        L.spectroHeight
+    };
+    return L;
+}
+
 // Reset all per-signal state after a new signal has been loaded into app.signal.
 // Drops the cached STFT/FFT-size cache and the on-screen textures so the main
 // loop recomputes from scratch (loadingPhase 0 handles the STFT (re)alloc).
@@ -260,22 +297,17 @@ int main(int argc, char* argv[])
         // View controls
         if (app.loaded && !UiModalOpen()) {
             // Spectrogram area fills remaining window space (scaled)
-            float viewScale = GetUIScale();
-            float sidebarWidth = 320 * viewScale;
-            float labelHeight = 15 * viewScale;
-            float scrollbarHeight = 18 * viewScale;
-            float freqLabelWidth = 65 * viewScale;
-            float vScrollbarWidth = 18 * viewScale;
-            float topMargin = 50 * viewScale;
-            float bottomMargin = 10 * viewScale;
-
-            float spectroHeight = (GetScreenHeight() - topMargin - bottomMargin - labelHeight - scrollbarHeight - 10 * viewScale) * ScopeDivider();
-            Rectangle viewBounds = {
-                sidebarWidth + freqLabelWidth,
-                topMargin,
-                GetScreenWidth() - sidebarWidth - freqLabelWidth - vScrollbarWidth - 20 * viewScale,
-                spectroHeight
-            };
+            Layout L = ComputeLayout();
+            float viewScale = L.scale;
+            float sidebarWidth = L.sidebarWidth;
+            float labelHeight = L.labelHeight;
+            float scrollbarHeight = L.scrollbarHeight;
+            float freqLabelWidth = L.freqLabelWidth;
+            float vScrollbarWidth = L.vScrollbarWidth;
+            float topMargin = L.topMargin;
+            float bottomMargin = L.bottomMargin;
+            float spectroHeight = L.spectroHeight;
+            Rectangle viewBounds = L.viewBounds;
 
             // Zoom with mouse wheel (zooms both time and frequency to maintain aspect ratio)
             if (GetMousePosition().x > sidebarWidth + 5 && CheckCollisionPointRec(GetMousePosition(), viewBounds)) {
@@ -478,22 +510,17 @@ int main(int argc, char* argv[])
         }
         
         // Selection: box select with LMB drag, right-click to clear
-        float selScale = GetUIScale();
-        float selSidebarWidth = 320 * selScale;
-        float selLabelHeight = 15 * selScale;
-        float selScrollbarHeight = 18 * selScale;
-        float selFreqLabelWidth = 65 * selScale;
-        float selVScrollbarWidth = 18 * selScale;
-        float selTopMargin = 50 * selScale;
-        float selBottomMargin = 10 * selScale;
-
-        float selSpectroHeight = (GetScreenHeight() - selTopMargin - selBottomMargin - selLabelHeight - selScrollbarHeight - 10.0f * selScale) * ScopeDivider();
-        Rectangle selBounds = {
-            selSidebarWidth + selFreqLabelWidth,
-            selTopMargin,
-            GetScreenWidth() - selSidebarWidth - selFreqLabelWidth - selVScrollbarWidth - 20.0f * selScale,
-            selSpectroHeight
-        };
+        Layout selL = ComputeLayout();
+        float selScale = selL.scale;
+        float selSidebarWidth = selL.sidebarWidth;
+        float selLabelHeight = selL.labelHeight;
+        float selScrollbarHeight = selL.scrollbarHeight;
+        float selFreqLabelWidth = selL.freqLabelWidth;
+        float selVScrollbarWidth = selL.vScrollbarWidth;
+        float selTopMargin = selL.topMargin;
+        float selBottomMargin = selL.bottomMargin;
+        float selSpectroHeight = selL.spectroHeight;
+        Rectangle selBounds = selL.viewBounds;
         Vector2 mousePos = GetMousePosition();
         
         // Calculate divider screen position (for hover detection)
@@ -766,23 +793,18 @@ int main(int argc, char* argv[])
         ClearBackground((Color){ 30, 30, 30, 255 });
 
         // Layout: sidebar on left, spectrogram on right (scaled)
-        float renderScale = GetUIScale();
-        float sidebarWidth = 320 * renderScale;
-        float labelHeight = 15 * renderScale;
-        float scrollbarHeight = 18 * renderScale;
-        float freqLabelWidth = 65 * renderScale;
-        float vScrollbarWidth = 18 * renderScale;
-        float topMargin = 50 * renderScale;
-        float bottomMargin = 10 * renderScale;
-
         // Spectrogram area (excludes labels and scrollbars)
-        float spectroHeight = (GetScreenHeight() - topMargin - bottomMargin - labelHeight - scrollbarHeight - 10 * renderScale) * ScopeDivider();
-        Rectangle viewBounds = {
-            sidebarWidth + freqLabelWidth,
-            topMargin,
-            GetScreenWidth() - sidebarWidth - freqLabelWidth - vScrollbarWidth - 20 * renderScale,
-            spectroHeight
-        };
+        Layout L = ComputeLayout();
+        float renderScale = L.scale;
+        float sidebarWidth = L.sidebarWidth;
+        float labelHeight = L.labelHeight;
+        float scrollbarHeight = L.scrollbarHeight;
+        float freqLabelWidth = L.freqLabelWidth;
+        float vScrollbarWidth = L.vScrollbarWidth;
+        float topMargin = L.topMargin;
+        float bottomMargin = L.bottomMargin;
+        float spectroHeight = L.spectroHeight;
+        Rectangle viewBounds = L.viewBounds;
         // Time labels sit just below the spectrogram
         Rectangle timeLabelArea = { viewBounds.x, viewBounds.y + viewBounds.height, viewBounds.width, labelHeight };
         // Horizontal scrollbar sits below the time labels