Mm to inches converter
Millimeters to inches with fractions, and inches back to mm
Type in either box. The example turns 10 mm into inches.
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- Nearest 1/16 inch
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- Nearest 1/32 inch
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- Centimeters
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The rule
One inch is exactly 25.4 millimeters (NIST Handbook 44, Appendix C, from the 1959 international agreement). Millimeters to inches: divide by 25.4. Inches to millimeters: multiply by 25.4. The second direction is always exact; the first usually needs rounding.
Worked example
10 mm ÷ 25.4 = 0.393701 inches. The nearest sixteenth is 6/16, which is 3/8 inch (0.375 in, 9.525 mm), and the nearest thirty-second is 13/32 (0.40625 in, 10.32 mm). Going back, 3/8 × 25.4 = 9.525 mm.
Fractions for tools
Drill bits, sockets, wrenches and pipe in the US are sized in fractions of an inch. The answer card shows the nearest 1/16 and 1/32. A metric size never matches an inch size exactly, so when a part must fit, check the exact figure: a 10 mm socket is slightly larger than 3/8 inch and will be loose on a 3/8 nut. You can type fractions such as 5/16 or 1 1/4 in the inches box.
A quick check
25 mm is just under an inch, and 100 mm is just under 4 inches (3.937). The chart below lists the common fractions from 1/16 to 2 inches. For centimeters, see mm to cm.
Rounding
The answer is worked out from the exact definition, then shown to 4 decimal places (6 significant figures for numbers below 1). It says "exactly" only when nothing was rounded.
Mm and inch fractions chart
Worked out from the exact definitions and rounded as above.
| Millimeters | Inches |
|---|---|
| 1 mm | 0.0393701 in |
| 2 mm | 0.0787402 in |
| 3 mm | 0.11811 in |
| 4 mm | 0.15748 in |
| 5 mm | 0.19685 in |
| 6 mm | 0.23622 in |
| 8 mm | 0.314961 in |
| 10 mm | 0.393701 in |
| 12 mm | 0.472441 in |
| 13 mm | 0.511811 in |
| 15 mm | 0.590551 in |
| 16 mm | 0.629921 in |
| 19 mm | 0.748031 in |
| 20 mm | 0.787402 in |
| 22 mm | 0.866142 in |
| 25 mm | 0.984252 in |
| 30 mm | 1.1811 in |
| 50 mm | 1.9685 in |
| 100 mm | 3.937 in |
| Inches | Millimeters |
|---|---|
| 1/16 in | 1.5875 mm |
| 1/8 in | 3.175 mm |
| 3/16 in | 4.7625 mm |
| 1/4 in | 6.35 mm |
| 5/16 in | 7.9375 mm |
| 3/8 in | 9.525 mm |
| 7/16 in | 11.1125 mm |
| 1/2 in | 12.7 mm |
| 5/8 in | 15.875 mm |
| 3/4 in | 19.05 mm |
| 7/8 in | 22.225 mm |
| 1 in | 25.4 mm |
| 1 1/4 in | 31.75 mm |
| 1 1/2 in | 38.1 mm |
| 2 in | 50.8 mm |