Convert Inches (in) to Millimeters (mm)
Convert inches (in) to millimetres (mm): multiply by 25.4, since 1 inch = 25.4 mm exactly. Handy for turning imperial drawings, screen sizes and hardware specs into metric.
Formula
1 in = 25.4 mm
To convert in to mm, multiply the value by 25.4.
Conversion Table
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.01 in | 0.254 mm |
| 0.1 in | 2.54 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 15 in | 381 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
| 250 in | 6350 mm |
| 500 in | 12700 mm |
| 1000 in | 25400 mm |
| 2500 in | 63500 mm |
| 5000 in | 127000 mm |
| 10000 in | 254000 mm |
| 50000 in | 1270000 mm |
Common in to mm Examples
- 1 in = 25.4 mm
- 5 in = 127 mm
- 10 in = 254 mm
- 25 in = 635 mm
- 50 in = 1270 mm
- 100 in = 2540 mm
- 500 in = 12700 mm
- 1000 in = 25400 mm
About in to mm
Because 1 in = 25.4 mm exactly, inches times 25.4 gives millimetres — 6 in = 152.4 mm. No rounding is needed, as the definition is exact.
It comes up constantly in manufacturing and DIY: a half-inch pipe is 12.7 mm, a 15-inch laptop screen is 381 mm diagonally, and US fastener sizes convert straight to mm for metric tooling.
Frequently Asked Questions
Where does the unit in come from?
Inches is a standard Length unit used in specific regions or fields. Its definition has been refined over time to match international measurement standards.
Where does the unit mm come from?
Millimeters is a Length unit with its own historical and regional roots, now defined in relation to internationally agreed reference standards.
How much is 1 in in mm?
1 in equals 25.4 mm. This ratio applies to every conversion between the two units.
What is the formula to convert in to mm?
The formula is 1 in = 25.4 mm. To convert any value, multiply the value by 25.4.
How do I convert in to mm by hand?
Take the value in in and multiply the value by 25.4. The result is the same value expressed in mm.
Is the conversion from in to mm exact?
The ratio 25.4 is defined to high precision and is exact for most practical purposes. Rounding only matters when many decimal places are needed.