Inches to Millimeters
An inch is exactly 2.54 centimeters, used for screen sizes, paper formats, and everyday measurements in the US. A millimeter is one thousandth of a meter, the standard unit on rulers and rainfall gauges worldwide. 1 in equals 25.4 mm, so converting between them is a matter of multiplying by that fixed factor — type any value into the converter below and both sides update instantly as you type.
Both units belong to length, measured here against length's base unit (m) — every other length unit on this site converts through that same reference point, which is why the table below can also be read as a quick cross-check against nearby values.
Formula
mm = in × 25.4
in = mm × ≈0.0393701
Worked example: 5 in × 25.4 = 127 mm.
Conversion table
| Inch (in) | Millimeter (mm) |
|---|---|
| 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
- How many Millimeters in a inch?
- 1 in equals 25.4 mm.
- How do I convert Inches to Millimeters?
- Multiply the value in in by 25.4 to get mm. The converter above does this instantly as you type.
- Is the conversion exact?
- Yes — Inch and Millimeter are both defined by a fixed conversion factor to length's base unit (m), so the result shown is exact to the precision displayed, not an approximation.