Quick answer
How to convert mm to inches
Divide the number of millimeters by 25.4. This is exact because one international inch is defined as exactly 25.4 millimeters.
Example: 100 mm to inches
100 / 25.4 = 3.93700787 inches, usually rounded to 3.937 inches.
Reference
MM to inches conversion table
These common values use the exact 25.4 conversion factor. Decimal results are rounded for display.
| Millimeters | Decimal inches | Fractional inches |
|---|---|---|
| 0.1 mm | 0.003937 in | About 0 in |
| 1 mm | 0.039370 in | About 3/64 in |
| 2 mm | 0.078740 in | About 5/64 in |
| 3 mm | 0.118110 in | About 1/8 in |
| 5 mm | 0.196850 in | About 13/64 in |
| 10 mm | 0.393701 in | About 25/64 in |
| 20 mm | 0.787402 in | About 25/32 in |
| 25 mm | 0.984252 in | About 63/64 in |
| 25.4 mm | 1 in | 1 in |
| 50 mm | 1.968504 in | About 1 31/32 in |
| 100 mm | 3.937008 in | About 3 15/16 in |
| 254 mm | 10 in | 10 in |
| 500 mm | 19.685039 in | About 19 11/16 in |
| 1,000 mm | 39.370079 in | About 39 3/8 in |
Metric bridge
MM to cm to inches
To convert millimeters to centimeters, divide by 10. Then divide centimeters by 2.54 to get inches.
- MM to cm: centimeters = millimeters / 10
- CM to inches: inches = centimeters / 2.54
Example: 254 mm = 25.4 cm = 10 inches. You can also use the dedicated mm to cm converter and cm to inches converter.
Decimal or fraction
Converting millimeters to inch fractions
Technical drawings normally use decimal inches. Woodworking and hardware sizes often use fractions such as 1/8, 1/16, 1/32, or 1/64 inch. This calculator rounds the decimal result to the nearest 1/64 inch for a practical fraction.
Use the decimal value when precision matters. A rounded fraction is easier to read on a tape measure, but it is not always exact.
Explore more
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Questions
MM to inches FAQ
How many inches are in 1 mm?
1 mm equals approximately 0.0393701 inches.
How many millimeters are in 1 inch?
1 inch equals exactly 25.4 millimeters.
Do I multiply or divide to convert mm to inches?
Divide millimeters by 25.4. To convert inches back to millimeters, multiply by 25.4.
Is 25 mm the same as 1 inch?
Not exactly. 25 mm is about 0.984252 inches. One inch is exactly 25.4 mm.
Why does the fraction differ from the decimal?
The decimal is calculated from the exact conversion. The fraction is rounded to the nearest 1/64 inch so it is practical to use with common measuring tools.