Inches to Millimeters Converter
1 inch = 25.4 millimeters
1 inch equals 25.4 millimeters
How to convert inches to millimeters
Feet, inches, yards and miles use the international foot (0.3048 m). Older US survey-foot records use a different definition; check the survey document before applying these factors.
mm = in × 127/5One inch is 127/5 millimeters, so a single multiplication converts any value.
254 mm = 10 × 127/5Inches to millimeters conversion table
Common values in inches, converted to millimeters.
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 10 | 254 |
| 20 | 508 |
| 25 | 635 |
| 50 | 1,270 |
| 100 | 2,540 |
| 250 | 6,350 |
| 500 | 12,700 |
| 1,000 | 25,400 |
About these units
inchin
Exactly 2.54 centimetres since the 1959 international agreement.
Reference: International Yard and Pound Agreement (1959).
millimetermm
One thousandth of a metre, the usual unit for engineering drawings.
Sources and precision
Table results are rounded to 8 significant digits; formula constants may be rounded to 10. Worked example answers use 6 significant digits. The converter starts at 6 significant digits and lets you change display precision. Calculations use the stored factors without intermediate rounding. Exact unit definitions do not make an input measurement more precise; conventional and measured factors follow the assumptions stated here.