diff --git a/src/engine/edge.test.ts b/src/engine/edge.test.ts
index 8f5517b..6c82046 100644
--- a/src/engine/edge.test.ts
+++ b/src/engine/edge.test.ts
@@ -219,4 +219,9 @@ describe("review fixes", () => {
   it("random() participates in arithmetic", () => {
     expect(calc("random() + 1")).not.toBeNull();
   });
+  it("multiplying same-dimension quantities converts the right operand", () => {
+    expect(calc("2 kg * 500 g")).toBe("1 kg");
+    expect(calc("$12 * 3")).toBe("$36");
+    expect(calc("2 m * 3 m")).toBe("6 m²");
+  });
 });
diff --git a/src/engine/evaluator.ts b/src/engine/evaluator.ts
index 2dc95ca..c34631d 100644
--- a/src/engine/evaluator.ts
+++ b/src/engine/evaluator.ts
@@ -252,6 +252,8 @@ function evalBin(op: "plus" | "minus" | "mul" | "div" | "mod" | "pow", l: Value,
           const u = ctx.reg.unitsById.get(targetId);
           if (u) return qty(baseProduct.div(u.ratio), u);
         }
+        // same dimension: "2 kg * 500 g" scales in the left unit, not 2*500
+        if (da === db) return qty(a.value.mul(convertQ(b, a.unit).value), a.unit);
         return qty(a.value.mul(b.value), a.unit);
       }
       return qty(a.value.mul(b.value), a.unit ?? b.unit ?? null);