Convert inches to millimeters
1 in = 25.4 mm — exactly. Both units are defined against the SI, so this factor is a fraction, not an approximation.
25.4mm
As a fraction: 127/5
1 in = 25.4 mm
How to convert inches to millimeters
Multiply the number of inches by 25.4 to get millimeters.
The exact factor is 25.4 — as a fraction, 127/5.
Inch: Defined as exactly 25.4 mm by the 1959 international yard and pound agreement.
Inch to Millimeter conversion table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 in | 25.4 |
| 2 in | 50.8 |
| 3 in | 76.2 |
| 5 in | 127 |
| 10 in | 254 |
| 20 in | 508 |
| 25 in | 635 |
| 50 in | 1270 |
| 100 in | 2540 |
| 250 in | 6350 |
| 500 in | 12 700 |
| 1000 in | 25 400 |
Millimeter to Inch conversion table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 mm | 0.039 370 079 |
| 2 mm | 0.078 740 157 |
| 3 mm | 0.118 110 24 |
| 5 mm | 0.196 850 39 |
| 10 mm | 0.393 700 79 |
| 20 mm | 0.787 401 57 |
| 25 mm | 0.984 251 97 |
| 50 mm | 1.968 503 9 |
| 100 mm | 3.937 007 9 |
| 250 mm | 9.842 519 7 |
| 500 mm | 19.685 039 |
| 1000 mm | 39.370 079 |
Frequently asked
How many millimeters are in a inch?
One inch equals 25.4 millimeters (in → mm). That figure is exact, not rounded.
How do you convert inches to millimeters?
Multiply the number of inches by 25.4 to get millimeters.
What is 1 mm in inches?
One millimeter is 0.03937007874 inches.
What is 10 in in mm?
10 in = 254 mm.
What exactly is a inch?
Defined as exactly 25.4 mm by the 1959 international yard and pound agreement.