Divide millimeters by 25.4 to get inches. One inch is defined as exactly 25.4 mm, so the result is as exact as the number you enter.
Millimeters to inches table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.03937008 |
| 2 | 0.07874016 |
| 3 | 0.1181102 |
| 4 | 0.1574803 |
| 5 | 0.1968504 |
| 6 | 0.2362205 |
| 7 | 0.2755906 |
| 8 | 0.3149606 |
| 9 | 0.3543307 |
| 10 | 0.3937008 |
| Millimeters (mm) | Inches (in) |
|---|---|
| 12 | 0.4724409 |
| 15 | 0.5905512 |
| 20 | 0.7874016 |
| 25 | 0.984252 |
| 30 | 1.181102 |
| 40 | 1.574803 |
| 50 | 1.968504 |
| 60 | 2.362205 |
| 75 | 2.952756 |
| 100 | 3.937008 |
Nearest fraction of an inch
US tools and hardware come in fractions, so a decimal like 0.354 in is not much use on its own. Multiply the decimal inches by 16, round to a whole number and put it over 16. 9 mm is 0.354 in; 0.354 × 16 = 5.67, so the nearest sixteenth is 6/16, which reduces to 3/8 in.
The full list of sixteenths with their millimeter values is on inches to mm.
If a sixteenth is not fine enough, use thirty-seconds or sixty-fourths the same way. Machinists often skip fractions and work in thousandths of an inch instead.
Do
- Use the wrench made for the bolt's system: a 10 mm nut needs a 10 mm wrench.
- Switch calipers to millimeter mode for parts thinner than 1/32 in.
Avoid
- Putting a 13 mm wrench on a 1/2 in (12.7 mm) nut. It is 0.3 mm loose and can round the corners.
- Trusting the nearest fraction when a fit has to be tight.
Where millimeters meet inches
Rain gauges, camera sensors and 3D printer settings use millimeters, while US lumber and plumbing are sold in inches. Watch cases are usually measured in millimeters; a 40 mm case is 1.57 in across. Paper sizes cross over too: an A4 sheet is 8.27 × 11.69 in, and cm to inches lists a few more.
For 3D printing and machining, keep the model and the machine in the same unit. A part drawn in inches but imported as millimeters comes out 25.4 times too small, a common surprise with STL files, which store no unit at all.
One millimeter in other length units
One millimeter in every other length unit on this site
- Centimeters0.1 cm
- Meters0.001 m
- Kilometers0.000001 km
- Inches0.039370079 in
- Feet0.0032808399 ft
- Yards0.0010936133 yd
- Miles6.2137119E-7 mi
Mm to inches questions
How many inches is 10 mm?
10 mm is 0.3937 in, a little more than 3/8 in.
Is 6 mm a quarter inch?
Close, but smaller. 1/4 in is 6.35 mm, so 6 mm is 0.236 in, about 0.35 mm short.
What is 100 mm in inches?
100 mm is 3.937 in, just under 4 in.
How many mm in 1/2 inch?
Half an inch is exactly 12.7 mm.
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