Inches To Mm Converter

Common in to mm conversions

How this conversion works

1 inch = 25.4 millimeters. Multiply inches by 25.4.

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Why this conversion is exact

The exact factor behind this page: 1 in = 25.4 mm. That value is a defined standard, not a measurement, so every conversion on this page is exact up to the digits shown. The most common practical error is mixing up which direction the factor runs: multiply when going from in to mm, divide when returning.

Rounding is display-only. The converter keeps full precision internally, so chained conversions (this unit to another and back) return to the starting value without drift, which hand-rounded tables cannot promise.

What you are converting

Inch

An inch is 1/12 of a foot, exactly 25.4 mm. Real-world anchor: a US quarter is about 1 inch wide.

Millimeter

A millimeter is 1/1,000 of a meter. Real-world anchor: a standard paper clip wire is about 1 mm thick.

Why convert and when you would use this

Reverse hardware conversion — US tools measured in inches used on metric parts.

Worked example

Worked example: 10 in × 25.4 = 254 mm.

Rounding and accuracy

Use 2–4 decimal places for everyday tasks; keep more for engineering or lab precision.

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