This mm to inches converter turns millimeters into inches the moment you type, with the exact factor the inch has been defined by since 1959. It helps when a metric drawing meets an imperial toolbox, when a product listing gives a thickness in mm, or when a ruler has only one scale on the side you can read. It runs in your browser and spends no credits.
How many inches are in a millimeter
One millimeter is 0.03937 inches. Put the other way, one inch is exactly 25.4 mm, so a millimeter is a little under 1/25 of an inch. That is why small metric sizes look so tiny once converted: 3 mm is only about 0.118 in.
MM to inches formula
Divide the millimeters by 25.4:
inches = mm ÷ 25.4
Multiplying by 0.03937 gives nearly the same answer, but dividing by 25.4 is exact. The converter uses the exact definition and shows results up to 8 significant digits.
Millimeters to inches chart
| Millimeters | Inches |
|---|---|
| 1 mm | 0.0394 in |
| 2 mm | 0.0787 in |
| 3 mm | 0.1181 in |
| 5 mm | 0.1969 in |
| 6 mm | 0.2362 in |
| 8 mm | 0.3150 in |
| 10 mm | 0.3937 in |
| 12 mm | 0.4724 in |
| 16 mm | 0.6299 in |
| 19 mm | 0.7480 in |
| 25 mm | 0.9843 in |
| 50 mm | 1.9685 in |
| 100 mm | 3.9370 in |
| 300 mm | 11.8110 in |
Worked example: a metric socket in an imperial set
Say a bolt head takes a 19 mm socket and your set is marked in fractions of an inch. 19 ÷ 25.4 = 0.7480 in. The nearest fraction, 3/4 in, is 0.75 in, only 0.002 in larger, which is why a 3/4 socket often fits a 19 mm head. The same check helps with drill bits and screws: a 10 mm bit is 0.3937 in, a hair larger than a 3/8 in bit (0.375 in), so the two are not interchangeable when a tight fit matters.
Reading mm on a ruler
On a metric ruler each small tick is 1 mm and each numbered line is 10 mm (1 cm). If you only have an inch ruler, 25 mm lands just short of the 1 in mark (0.9843 in), and 300 mm is a bit under a foot (11.811 in).
FAQ
Is 25 mm the same as 1 inch?
Close, but no. 25 mm is 0.9843 in. One inch is 25.4 mm, so 25 mm is 0.4 mm short.
How do I convert inches back to mm?
Type in the Inches box, or press swap. Multiply inches by 25.4 to do it by hand.
What does it cost?
It comes with the Nexin library: Nexin Lite or Nexin Pro opens it, and it spends no credits.
