MM to Inches Converter

Enter a measurement in millimetres to see the equivalent in inches. Common for engineering drawings and product specs.

How it works

The inch is defined as 25.4 millimetres exactly (2.54 cm × 10). Dividing millimetres by 25.4 yields inches with no conversion-chart rounding. 25.4 mm is 1 inch; 100 mm is about 3.9370 inches. This is finer-grained than the centimetre converter but uses the same international definition.

Formula

inches = millimetres ÷ 25.4

Worked examples

25.4 mm → 1 in
100 mm → 3.9370 in

Useful notes

1 inch = 25.4 mm exactly.
For centimetres, use CM to Inches (divide by 2.54) instead of converting mm to cm first.

FAQ

How many inches are in 1 mm?: About 0.03937 inches (1 ÷ 25.4).
Is 25.4 mm exactly one inch?: Yes. The international inch is defined as 25.4 millimetres.
Should I use mm or cm?: Use millimetres when the drawing is dimensioned in mm. Centimetres are the same conversion scaled by 10.

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