CM Ruler — 30 cm Actual Size

We identify your screen from its pixel signature and apply factory PPI. Works for 250+ phones, tablets and laptops.

Select exact model for factory-precise PPI.

Enter your screen diagonal (find on box or search “MacBook Air 13.6 specs”). We calculate PPI from native resolution.

Any bank card is 85.60 × 53.98 mm (ISO ID-1). Place it on the blue rectangle below and drag slider until they match. This sidesteps zoom and scaling errors.