Inches to millimeters
1 inch = 25.4 millimeters
For any other value: mm = in × 25.4
Calculator
25.4 mm
Type a number — fractions like 3/8 or 1 1/2 work too.
You can leave the unit in: 100 in is fine.
Inches to millimeters chart
The values people look up most.
| inches | millimeters |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 8 in | 203.2 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 5 in | 127 mm |
| 16 in | 406.4 mm |
| 11 in | 279.4 mm |
| 32 in | 812.8 mm |
| 7 in | 177.8 mm |
| 9 in | 228.6 mm |
| 13 in | 330.2 mm |
| 18 in | 457.2 mm |
| 2.5 in | 63.5 mm |
| 1.5 in | 38.1 mm |
| 6 in | 152.4 mm |
| 34 in | 863.6 mm |
| 1.25 in | 31.75 mm |
| 3.5 in | 88.9 mm |
| 25 in | 635 mm |
| 12 in | 304.8 mm |
| 75 in | 1905 mm |
| 55 in | 1397 mm |
| 4.5 in | 114.3 mm |
| 5.5 in | 139.7 mm |
| 2.25 in | 57.15 mm |
| 10 in | 254 mm |
| 14 in | 355.6 mm |
| 20 in | 508 mm |
| 24 in | 609.6 mm |
| 1/2 in | 12.7 mm |
| 1/4 in | 6.35 mm |
| 3/8 in | 9.525 mm |
| 5/8 in | 15.875 mm |
| 5/16 in | 7.9375 mm |
| 3/4 in | 19.05 mm |
| 7/8 in | 22.225 mm |
| 1/8 in | 3.175 mm |
| 3/16 in | 4.7625 mm |
| 7/16 in | 11.1125 mm |
Formula
mm = in × 25.4
In inches, fractions carry as much weight as whole numbers — 1/2, 3/8 and 1/4 are among the most looked-up sizes.
Where this number comes from
This factor is exact, not rounded. The inch is exactly 25.4 mm under the 1959 international yard and pound agreement — not a rounded figure.
Source: NIST Guide to the SI, Appendix B: Conversion Factors, NIST (National Institute of Standards and Technology, USA).
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