Convert Inch to Millimeter
Convert Inch to Millimeter instantly. 1 in = 25.4 mm. Formula, worked examples and a quick reference table.
Last updated
One inch equals 25.4 millimeters. To convert any number of inchs to millimeters, multiply by 25.4.
The converter above works in both directions and updates as you type. Below you will find the formula, a worked example and a reference table of common values.
Inch to Millimeter formula
To go the other way, use inch = millimeter ÷ 25.4.
About these units
The inch has been defined as exactly 25.4 millimetres since the 1959 international yard and pound agreement, which finally reconciled slightly different British and American definitions.
Inch to Millimeter conversion table
| Inch | Millimeter |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
| 250 in | 6,350 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
Frequently asked questions
How many millimeters are in a inch? +
There are 25.4 millimeters in one inch.
What is 10 in in mm? +
10 in equals 254 mm. Multiply 10 by 25.4.
How do I convert millimeter back to inch? +
Use inch = millimeter ÷ 25.4. The converter above handles both directions, or see our dedicated Millimeter to Inch page.