Convert Inch to Millimetre
Turn inches into Millimetres in an instant. Type a value below to get an accurate in → mm result, with the formula and a quick-reference table.
1 in = 25.4 mm
Quick answer: 1 Inch = 25.4 Millimetre
Inch to Millimetre conversion table
| Inch (in) | Millimetre (mm) |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
How to convert Inch to Millimetre
To convert inches to Millimetres, multiply the value by 25.4.
- Take your measurement in inches.
- Multiply it by 25.4 — the number of Millimetres in one Inch.
- The result is the same amount, expressed in Millimetres.
To go the other way, multiply Millimetres by 0.039370079 — or simply divide by 25.4.
For example, a US quarter coin is about 1 in, which is 25.4 mm.
About Inch and Millimetre
An inch is an imperial unit of length defined as exactly 2.54 centimetres, or one-twelfth of a foot. It is standard in the United States for screen sizes, lumber, pipe diameters and everyday measurements.
A millimetre is one-thousandth of a metre (1/1000 m) — the smallest line printed on a standard ruler. It is the everyday unit for fine measurements such as engineering tolerances, screw threads, paper thickness and rainfall.
The Inch is a imperial / US customary unit while the Millimetre comes from the metric system — which is exactly why this conversion comes up so often. One Inch equals 25.4 Millimetres.
Other length conversions
Frequently asked questions
How many Millimetres are in a Inch?
1 Inch equals 25.4 Millimetre (in → mm). To convert any amount, multiply the number of inches by 25.4.
How do I convert Inch to Millimetre?
Enter the number of inches in the converter above and read the result in Millimetres. It applies the exact in → mm factor instantly, with full precision.
Is the Inch to Millimetre converter free?
Yes — it is completely free and unlimited, needs no sign-up, and runs right in your browser, so it is instant and private.
Is the conversion accurate?
Yes. It uses the internationally defined length factors and full floating-point precision, then rounds the display to a clean, readable number.