How Many mm in an Inch?

There are 25.4 millimeters in an inch. This is an exact conversion factor used internationally since 1959.

How many mm in an inch? — see the answer and conversion table below.

Use the related converter below for custom values.

Formula

Answer: There are 25.4 millimeters in an inch. This is an exact conversion factor used internationally since 1959.

Example

Question: How many mm in an inch? Answer: There are 25.4 millimeters in an inch. This is an exact conversion factor used internationally since 1959.

How to Use

  1. Read the direct answer at the top of the page
  2. Check the conversion table for common values
  3. Use the related converter for custom values
  4. Browse the FAQ for common follow-up questions

Frequently Asked Questions

Is 25.4 mm exactly 1 inch?

Yes. Since 1959, 1 inch has been defined as exactly 25.4 millimeters. This is an international standard.

How many mm in 10 inches?

There are 254 mm in 10 inches (10 x 25.4).

How many mm in a foot?

There are 304.8 mm in 1 foot (12 x 25.4).

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Author: Calczy Editorial Team Reviewed by: Calczy Editorial Team Last updated: 2026-09-16

This page was reviewed for accuracy by the Calczy editorial team. Our editorial process follows our editorial policy to ensure reliable, up-to-date conversion tools and reference content.