diff --git a/HellionChat/Ui/StyleEngine/TypeScaleMath.cs b/HellionChat/Ui/StyleEngine/TypeScaleMath.cs
new file mode 100644
index 0000000..79a6fb4
--- /dev/null
+++ b/HellionChat/Ui/StyleEngine/TypeScaleMath.cs
@@ -0,0 +1,13 @@
+namespace HellionChat.Ui.StyleEngine;
+
+// TEST-MIRROR: Ui/TypeScaleMathTests.cs
+//
+// Rounds to quarter points rather than whole ones. The base size itself is
+// 12.75pt, so whole-point rounding would move a role by more than the step
+// between two adjacent base sizes -- the scale would quantise away the very
+// difference it exists to express.
+internal static class TypeScaleMath
+{
+    internal static float Resolve(float basePt, float factor, float minPt) =>
+        MathF.Max(minPt, MathF.Round(basePt * factor * 4f) / 4f);
+}