mm to in – Millimetres to Inches Converter

How to convert millimetres to inches

One millimetre equals 0.03937 inches, so multiply the number of millimetres by 0.03937:

in = mm × 0.03937
mm = in ÷ 0.03937 (1 in = 25.4 mm)

Example: 3 mm → 3 × 0.03937 = 0.11811 in.

Going the other way, divide by 0.03937, or multiply by 25.4; the inches to millimetres converter does it for you.

Everyday values

Millimetres	Inches	For example
3 mm	0.11811 in	a 1/8-inch drill bit is about 3.2 mm
6 mm	0.23622 in	about 1/4 inch
10 mm	0.393701 in	1 cm
13 mm	0.511811 in	about 1/2 inch
19 mm	0.748031 in	about 3/4 inch
25.4 mm	1 in	exactly one inch

When you need this conversion

Millimetres are the standard unit in engineering, mechanics and manufacturing worldwide. Many tools, bolts and drill bits still come in fractional inches, so mechanics often need the nearest fraction. As a rule of thumb, 1/16 inch is about 1.6 mm, 1/8 inch about 3.2 mm, 1/4 inch about 6.35 mm and 1/2 inch 12.7 mm.

Millimetre to inch conversion table

mm	in	mm	in
1 mm	0.03937 in	16 mm	0.629921 in
2 mm	0.07874 in	17 mm	0.669291 in
3 mm	0.11811 in	18 mm	0.708661 in
4 mm	0.15748 in	19 mm	0.748031 in
5 mm	0.19685 in	20 mm	0.787402 in
6 mm	0.23622 in	21 mm	0.826772 in
7 mm	0.275591 in	22 mm	0.866142 in
8 mm	0.314961 in	23 mm	0.905512 in
9 mm	0.354331 in	24 mm	0.944882 in
10 mm	0.393701 in	25 mm	0.984252 in
11 mm	0.433071 in	26 mm	1.0236 in
12 mm	0.472441 in	27 mm	1.063 in
13 mm	0.511811 in	28 mm	1.1024 in
14 mm	0.551181 in	29 mm	1.1417 in
15 mm	0.590551 in	30 mm	1.1811 in

About the units

Millimetre (mm): one thousandth of a metre.
Inch (in): exactly 2.54 centimetres (international agreement of 1959).

Both are units of length. The conversion factor comes from the exact definitions above, so the calculator is exact; results are only rounded for display (up to six significant digits).

Frequently asked questions

How many inches are in one millimetre?

One millimetre is 0.03937 inches. One inch is 25.4 millimetres.

How do I convert millimetres to inches?

Multiply the value in millimetres by 0.03937. To go back, divide by 0.03937.

What is 3 mm in inches?

3 mm = 0.11811 in.

What is 6 mm in inches?

6 mm = 0.23622 in.

Sources

NIST Special Publication 811 (2008), Guide for the Use of the International System of Units (SI), Appendix B: conversion factors.
NIST Handbook 44 (2024), Appendix C: General tables of units of measurement.

Last reviewed 5 October 2026. Results are estimates; see our disclaimer.

Millimetres to Inches Converter