mm to inches formula
To convert millimeters to inches, multiply the number of millimeters by 0.0393700787402. In symbols: in = mm × 0.0393700787402.
One millimeter equals 0.0393700787402 inches, and one inch equals 25.4 millimeters. Since the inch is exactly 25.4 mm, one millimeter is exactly 0.0393700787 in.
Worked example
Suppose you have 25 millimeters and need the answer in inches.
- Write the formula: in = mm × 0.0393700787402.
- Put in the number: 25 × 0.0393700787402 = 0.9842519685.
- Round to suit the job. 0.9843 in is accurate enough for most everyday uses.
So 25 mm is 0.9842519685 in. To check, convert back: 0.9842519685 in is 25 mm.
Common millimeters to inches values
| millimeters (mm) | inches (in) |
|---|---|
| 1 | 0.03937007874 |
| 2 | 0.07874015748 |
| 5 | 0.1968503937 |
| 10 | 0.3937007874 |
| 20 | 0.7874015748 |
| 50 | 1.968503937 |
| 100 | 3.937007874 |
Reference points
Some familiar amounts in millimeters, converted to inches:
- 3 mm, a drill bit: 0.11811 in
- 25.4 mm, exactly one inch: 1 in
- 35 mm, the width of classic film: 1.37795 in
- 100 mm, ten centimeters: 3.93701 in
Where you will use it
Phone cases, lenses, drill bits and sheet sizes are specified in millimeters. US hardware shops and hobby tools often sell them in inches.
Quick mental math
Divide by 25. 25 mm is almost exactly one inch (0.984 in). Rule of thumb: multiply by 0.04. For 25 mm this gives 1 in against the exact 0.9843, an error of 1.6 percent.
Going the other way
Need the reverse? Use the inches to mm converter. For comparison, 1 in is 25.4 mm. To compare every length unit at once, open the length converter.
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