A browser-based ruler that renders measurements at true physical size— DPI
🎯 Calibrate your screen
Choose your device for exact DPI — no manual calibration needed.
No device selected yet.
🍎 MacBook Air
🍎 MacBook Pro
🍎 iMac / Studio / Pro Display
🪟 Windows / other laptops
Hold a credit card up against the blue rectangle on your screen. Drag the slider until they are exactly the same size. Credit cards are standardized at 85.6 × 54 mm.