mm to inches
Unit Converters

mm to inches

Convert millimeters to inches (or inches to millimeters) instantly. Type a value in either field and the other updates live; use the swap button to flip the direction.

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How It Works

One inch is exactly 25.4 millimeters, so to convert millimeters to inches you divide the number of millimeters by 25.4. To go the other way, multiply inches by 25.4.

Frequently Asked Questions

How many millimeters are in one inch?
One inch is exactly 25.4 millimeters. This is the official definition adopted internationally in 1959, so the conversion is exact.
Is 25.4 mm an exact or approximate value?
It is exact. The inch was redefined in 1959 to be exactly 25.4 millimeters, making conversions between imperial and metric length units precise.
How do I convert mm to inches in my head?
A quick approximation is to divide millimeters by 25. For better accuracy, divide by 25.4. For example, 100 mm ÷ 25.4 ≈ 3.94 inches.

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