Inches to MM Converter
Convert inch to millimeter instantly. 1 in = 25.4 mm, worked steps and a full reference table.
How to use it
- Type the value in inch — the result updates as you type.
- Use Swap to flip the direction, or change either dropdown to convert between any two units.
- Click the result to copy it. The URL updates too, so you can bookmark or share the exact conversion.
Examples
| 1 in | 25.4 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 100 in | 2540 mm |
One inch equals 25.4 millimeters (mm). To convert inches to millimeters, multiply by 25.4; to go back the other way, multiply by 0.039370079 instead.
The converter above does it as you type and shows the working underneath, so you can check the arithmetic rather than take the number on trust.
What inches and millimeters actually measure
Inch (in) — An inch is exactly 25.4 millimetres by international agreement since 1959. Screen sizes, pipe and tyre diameters, and construction in the US.
Millimeter (mm) — A millimetre is a thousandth of a metre, and the smallest division on a normal ruler. Engineering drawings, timber and steel sizes, rainfall and screen bezels.
Inches to MM conversion table
The most common values, worked out in advance. Anything not listed can be typed straight into the converter.
| in | mm |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 25 in | 635 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
How to convert inches to millimeters by hand
Multiply the number of inches by 25.4.
For example, 25 in × 25.4 = 635 mm.
Going the other way, divide by 25.4 — or multiply by 0.039370079, which is the same thing and easier to do in your head.
Everything runs in your browser
There is no server involved in the calculation. The numbers you type never leave your device, nothing is logged, and the page keeps working with no connection once it has loaded. That is not a marketing line — it is simply how the tool is built, because a calculation like this has no reason to touch a network.
Questions people ask
How many mm are in 1 in?
1 in equals exactly 25.4 mm. Multiply any value in inch by 25.4 to get millimeter.
Is anything uploaded to a server?
No. The whole calculation happens in your browser. Nothing is sent anywhere, and the page keeps working offline once loaded.
Last updated 18 August 2026