Inches to Millimeters
Convert inches (in) to millimeters (mm). 1 in = 25.4 mm (and 1 mm = 0.039370079 in). It all runs locally in your browser.
Inches to Millimeters table
| Inches | Millimeters |
|---|---|
| 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 |
| 25 in | 635 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
Where this conversion shows up
Workshop and hardware territory. Drill bits, screws, timber, camera filters and pipe fittings are specified in inches in the US and millimetres almost everywhere else, and getting it wrong means a part that does not fit.
Worked example
A ¼ inch drill bit is 0.25 × 25.4 = 6.35 mm, which is why a 6 mm bit leaves a hole slightly too tight and a 6.5 mm one slightly too loose. A 6×4 inch photo is 152.4 × 101.6 mm.
Rounding and precision
Do not round in engineering contexts: the difference between 6.35 mm and 6 mm is enough to ruin a fit. Fractional inches convert exactly — ⅛ in is 3.175 mm, ½ in is 12.7 mm.
How to convert
To convert inches to millimeters, multiply by 25.4. Need other units? Use the full Unit Converter.
FAQ
How many millimeters in a inche?
1 inche equals 25.4 millimeters (mm).
How do I convert inches to millimeters?
Multiply the inches value by 25.4. For example, 5 in = 127 mm.
How many mm in an inch?
Exactly 25.4 mm. The inch has been defined as exactly 25.4 millimetres since 1959, so every inch-to-millimetre conversion is exact.
What is 1/4 inch in mm?
6.35 mm. Similarly ⅛ in is 3.175 mm, ⅜ in is 9.525 mm and ½ in is 12.7 mm.