diff --git a/src/features/autoScale/.gitkeep b/src/features/autoScale/.gitkeep
deleted file mode 100644
index e69de29..0000000
diff --git a/src/features/autoScale/__tests__/calculateScale.test.ts b/src/features/autoScale/__tests__/calculateScale.test.ts
new file mode 100644
index 0000000..fdea04e
--- /dev/null
+++ b/src/features/autoScale/__tests__/calculateScale.test.ts
@@ -0,0 +1,48 @@
+import { calculateScale } from '../calculateScale';
+
+describe('calculateScale', () => {
+  it('사진 어깨 / 카메라 옷 너비 비율을 그대로 반환한다', () => {
+    const result = calculateScale({
+      photoShoulderPx: 200,
+      cameraClothWidthPx: 400,
+    });
+    expect(result.scale).toBe(0.5);
+    expect(result.confidence).toBeGreaterThan(0);
+  });
+
+  it('카메라 옷 너비가 0이면 scale=1, confidence=0으로 폴백한다', () => {
+    const result = calculateScale({
+      photoShoulderPx: 200,
+      cameraClothWidthPx: 0,
+    });
+    expect(result.scale).toBe(1);
+    expect(result.confidence).toBe(0);
+  });
+
+  it('카메라 옷 너비가 음수여도 0과 동일하게 폴백한다', () => {
+    const result = calculateScale({
+      photoShoulderPx: 200,
+      cameraClothWidthPx: -5,
+    });
+    expect(result.scale).toBe(1);
+    expect(result.confidence).toBe(0);
+  });
+
+  it('비율이 3.0을 초과하면 3.0으로 클램핑 + confidence 낮춤', () => {
+    const result = calculateScale({ photoShoulderPx: 200, cameraClothWidthPx: 10 });
+    expect(result.scale).toBe(3.0);
+    expect(result.confidence).toBeLessThan(1);
+  });
+
+  it('비율이 0.3 미만이면 0.3으로 클램핑 + confidence 낮춤', () => {
+    const result = calculateScale({ photoShoulderPx: 10, cameraClothWidthPx: 200 });
+    expect(result.scale).toBe(0.3);
+    expect(result.confidence).toBeLessThan(1);
+  });
+
+  it('클램핑 안 되는 정상 비율이면 confidence=1', () => {
+    const result = calculateScale({ photoShoulderPx: 200, cameraClothWidthPx: 200 });
+    expect(result.scale).toBe(1.0);
+    expect(result.confidence).toBe(1);
+  });
+});
diff --git a/src/features/autoScale/calculateScale.ts b/src/features/autoScale/calculateScale.ts
new file mode 100644
index 0000000..86b961a
--- /dev/null
+++ b/src/features/autoScale/calculateScale.ts
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+export interface ScaleInput {
+  photoShoulderPx: number;
+  cameraClothWidthPx: number;
+}
+
+export interface ScaleResult {
+  scale: number;
+  confidence: number;
+}
+
+export const MIN_SCALE = 0.3;
+export const MAX_SCALE = 3.0;
+
+export function calculateScale({ photoShoulderPx, cameraClothWidthPx }: ScaleInput): ScaleResult {
+  if (cameraClothWidthPx <= 0) {
+    return { scale: 1, confidence: 0 };
+  }
+  const raw = photoShoulderPx / cameraClothWidthPx;
+  const scale = Math.max(MIN_SCALE, Math.min(MAX_SCALE, raw));
+  const confidence = scale === raw ? 1 : 0.5;
+  return { scale, confidence };
+}