---
title: "Inches to Millimeters — in to mm converter"
description: "1 inch = 25.4 millimeters. Convert inches to millimeters with a full conversion table, the exact formula, and a calculator for any value."
url: https://atoneplace.net/convert/inches-to-mm/
site: "At One Place"
---

# Inches to millimeters

**1 inch in millimeters: 1 in = 25.4 mm**

mm = in × 25.4

To convert inches to millimeters, multiply by 25.4. The table below gives the values people look up most often, and the converter works for any number.

## Inches to millimeters table

*Common inch values converted to millimeters.*

| Inches | Millimeters |
| --- | --- |
| 1 in | 25.4 |
| 2 in | 50.8 |
| 3 in | 76.2 |
| 4 in | 101.6 |
| 5 in | 127 |
| 10 in | 254 |
| 15 in | 381 |
| 20 in | 508 |
| 25 in | 635 |
| 30 in | 762 |
| 40 in | 1,016 |
| 50 in | 1,270 |
| 75 in | 1,905 |
| 100 in | 2,540 |
| 250 in | 6,350 |
| 500 in | 12,700 |
| 1,000 in | 25,400 |

## How the conversion works

The relationship is mm = in × 25.4. Both units measure length, so the conversion is a fixed factor that never changes. The figure is exact rather than approximate: since the international yard and pound agreement of 1959, an inch is defined as exactly 25.4 millimetres and a pound as exactly 0.45359237 kilograms, and every other imperial and US customary unit here is derived from those two.

## Common questions

### How many millimeters are in one inch?

One inch equals 25.4 millimeters. mm = in × 25.4.

### How do you convert inches to millimeters?

Use mm = in × 25.4. So 10 in is 254 mm.

### How many inches are in one millimeter?

One millimeter equals 0.03937 inches, which is the reverse of the conversion above.

## Related pages

- [Millimeters to Inches](https://atoneplace.net/convert/mm-to-inches/)
- [Inches to Meters](https://atoneplace.net/convert/inches-to-meters/)
- [Inches to Kilometers](https://atoneplace.net/convert/inches-to-km/)
- [Inches to Centimeters](https://atoneplace.net/convert/inches-to-cm/)
- [Inches to Miles](https://atoneplace.net/convert/inches-to-miles/)
- [Inches to Yards](https://atoneplace.net/convert/inches-to-yards/)
- [Inches to Feet](https://atoneplace.net/convert/inches-to-feet/)

## Sources

- Guide for the Use of the International System of Units (SP 811) — NIST (https://www.nist.gov/pml/special-publication-811) [Public domain (US Government)]
- The International System of Units (SI Brochure) — Bureau International des Poids et Mesures (https://www.bipm.org/en/publications/si-brochure)
- Calculated on this page — At One Place (/about/)