diff --git a/HellionChat/Ui/StyleEngine/Metrics.cs b/HellionChat/Ui/StyleEngine/Metrics.cs
new file mode 100644
index 0000000..8ed96f0
--- /dev/null
+++ b/HellionChat/Ui/StyleEngine/Metrics.cs
@@ -0,0 +1,112 @@
+using Dalamud.Bindings.ImGui;
+using Dalamud.Interface.Utility;
+using HellionChat.Util;
+
+namespace HellionChat.Ui.StyleEngine;
+
+// Layout values, authored at 100% display scaling. Draw code reads the scaled
+// properties; the Raw constants exist only for the few places that must store or
+// compare an unscaled value (Sidebar.GetWidth, the width slider bounds).
+//
+// Deliberately NOT part of ThemeLayout: that record is serialised into theme
+// JSON, and layout customisation is out of scope per the master spec.
+internal static class Metrics
+{
+    // --- Sidebar ---
+    internal const float SidebarIconOnlyWidthRaw = 38f;
+    internal const float SidebarMinWidthRaw = 40f;
+    internal const float SidebarMaxWidthRaw = 300f;
+    internal const float SidebarRowHeightRaw = 32f;
+    internal const float SidebarPopOutHitWidthRaw = 22f;
+    internal const float SidebarGreetedHitWidthRaw = 22f;
+    internal const float SidebarHitSlackRaw = 4f;
+    internal const float SidebarMinDrawWidthRaw = 2f;
+    internal const float SidebarUnreadRadiusRaw = 4f;
+    internal const float SidebarGlyphInsetRaw = 4f;
+
+    // --- Input bar ---
+    internal const float InputBarHeightRaw = 32f;
+    internal const float InputPillHeightRaw = 22f;
+    internal const float InputPillPaddingXRaw = 8f;
+    internal const float InputPillRoundingRaw = 6f;
+    internal const float InputQuickButtonsReserveRaw = 130f;
+
+    // --- Honorific header ---
+    internal const float HonorificHeightRaw = 30f;
+    internal const float HonorificInsetRaw = 8f;
+    internal const float HonorificBracketGapRaw = 6f;
+
+    // --- Top tab bar ---
+    internal const float TopTabUnreadRadiusRaw = 3.5f;
+    internal const float TopTabUnreadInsetRaw = 4f;
+
+    // --- Status bar ---
+    internal const float StatusBorderThicknessRaw = 1f;
+    internal const float StatusTopSpacerRaw = 2f;
+    internal const float StatusMinOtherSlotsWidthRaw = 200f;
+    internal const float StatusDotRadiusRaw = 4f;
+
+    // --- Message list ---
+    internal const float MessageDummyWidthRaw = 10f;
+
+    private static float _cachedScale = 1f;
+    private static int _cachedFrame = -1;
+
+    // GlobalScale resolves to ImGui.GetIO().FontGlobalScale, which the Dalamud
+    // settings slider moves on every frame while it is dragged. Pinning it once
+    // per frame keeps a CalcSize and its matching Draw on the same value, and
+    // saves three native calls per access.
+    internal static float Scale
+    {
+        get
+        {
+            var frame = ImGui.GetFrameCount();
+            if (frame == _cachedFrame)
+                return _cachedScale;
+
+            _cachedFrame = frame;
+            _cachedScale = ImGuiHelpers.GlobalScale;
+            return _cachedScale;
+        }
+    }
+
+    internal static float SidebarIconOnlyWidth => MetricsMath.Scale(SidebarIconOnlyWidthRaw, Scale);
+    internal static float SidebarRowHeight => MetricsMath.Scale(SidebarRowHeightRaw, Scale);
+    internal static float SidebarPopOutHitWidth =>
+        MetricsMath.Scale(SidebarPopOutHitWidthRaw, Scale);
+    internal static float SidebarGreetedHitWidth =>
+        MetricsMath.Scale(SidebarGreetedHitWidthRaw, Scale);
+    internal static float SidebarHitSlack => MetricsMath.Scale(SidebarHitSlackRaw, Scale);
+    internal static float SidebarMinDrawWidth => MetricsMath.Scale(SidebarMinDrawWidthRaw, Scale);
+    internal static float SidebarUnreadRadius => MetricsMath.Scale(SidebarUnreadRadiusRaw, Scale);
+    internal static float SidebarGlyphInset => MetricsMath.Scale(SidebarGlyphInsetRaw, Scale);
+
+    internal static float InputBarHeight => MetricsMath.Scale(InputBarHeightRaw, Scale);
+    internal static float InputPillHeight => MetricsMath.Scale(InputPillHeightRaw, Scale);
+    internal static float InputPillPaddingX => MetricsMath.Scale(InputPillPaddingXRaw, Scale);
+    internal static float InputPillRounding => MetricsMath.Scale(InputPillRoundingRaw, Scale);
+    internal static float InputQuickButtonsReserve =>
+        MetricsMath.Scale(InputQuickButtonsReserveRaw, Scale);
+
+    internal static float HonorificHeight => MetricsMath.Scale(HonorificHeightRaw, Scale);
+    internal static float HonorificInset => MetricsMath.Scale(HonorificInsetRaw, Scale);
+    internal static float HonorificBracketGap => MetricsMath.Scale(HonorificBracketGapRaw, Scale);
+
+    internal static float TopTabUnreadRadius => MetricsMath.Scale(TopTabUnreadRadiusRaw, Scale);
+    internal static float TopTabUnreadInset => MetricsMath.Scale(TopTabUnreadInsetRaw, Scale);
+
+    internal static float StatusBorderThickness =>
+        MetricsMath.Scale(StatusBorderThicknessRaw, Scale);
+    internal static float StatusTopSpacer => MathF.Round(StatusTopSpacerRaw * Scale);
+    internal static float StatusMinOtherSlotsWidth =>
+        MetricsMath.Scale(StatusMinOtherSlotsWidthRaw, Scale);
+    internal static float StatusDotRadius => MetricsMath.Scale(StatusDotRadiusRaw, Scale);
+
+    internal static float MessageDummyWidth => MetricsMath.Scale(MessageDummyWidthRaw, Scale);
+
+    // Text-dependent heights are measured, never scaled: the font is built from
+    // Config.FontSizeV2, which GlobalScale does not feed into. StatusBar.Height
+    // has done it this way since 1.8.x.
+    internal static float CenterY(float rowHeight) =>
+        MetricsMath.CenterY(rowHeight, ImGui.GetTextLineHeight());
+}
diff --git a/HellionChat/Util/MetricsMath.cs b/HellionChat/Util/MetricsMath.cs
new file mode 100644
index 0000000..afedc0d
--- /dev/null
+++ b/HellionChat/Util/MetricsMath.cs
@@ -0,0 +1,13 @@
+namespace HellionChat.Util;
+
+// Pure scaling arithmetic, split out from Metrics so the build suite can pin it
+// without standing up an ImGui frame.
+internal static class MetricsMath
+{
+    internal static float Scale(float raw, float scale) => raw * scale;
+
+    // Vertical centering for text inside a fixed-height row. Frozen offsets keep
+    // their mis-centering at every other font size; a computed one does not.
+    internal static float CenterY(float rowHeight, float textHeight) =>
+        (rowHeight - textHeight) * 0.5f;
+}