MM to Inches Converter
Divide millimeters by 25.4 to get inches, because one inch is exactly 25.4 millimeters. 25.4 mm = 1 in, so a part that is 25.4 mm long is exactly one inch.
Millimeters are the usual unit for small parts and technical drawings, so the table below runs from a single millimeter up to a meter.
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(opens in a new tab)How to convert millimeters to inches
Formula: inches = millimeters / 25.4
The constant is exact by definition: 1 inch = 25.4 millimeters. It is not a rounded approximation.
Datasheets, drawings and manufacturing specifications list sizes in millimeters, while some hardware, tools and fittings are still sold in inches. Converting between them here gives a decimal inch, such as 1.96850393701 in, not a fraction.
Worked example: 50 mm to inches
The answer below is shown to 12 significant digits. The full value has more digits, so treat the displayed figure as rounded.
Convert 50 mm
Input
50 mm
Output
50 / 25.4 = 1.96850393701 in
Common millimeters to inches conversions
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 mm | 0.0393700787402 in |
| 2 mm | 0.0787401574803 in |
| 5 mm | 0.196850393701 in |
| 10 mm | 0.393700787402 in |
| 25 mm | 0.984251968504 in |
| 50 mm | 1.96850393701 in |
| 100 mm | 3.93700787402 in |
| 250 mm | 9.84251968504 in |
| 1000 mm | 39.3700787402 in |
When you need to convert millimeters to inches
- Small product dimensions: thickness of a phone or a laptop, listed in millimeters.
- Hardware: bolt, screw and bit sizes compared across metric and inch catalogs.
- Manufacturing and engineering drawings that mix metric and inch parts.
- Technical measurements such as the width of a sensor, a cable or a gasket.
Things worth knowing
- This converter gives decimal inches. It does not round to fractions such as 1/16 or 1/32, which many tape measures and drill-bit sets use. Rounding to a fraction depends on the tolerance you need.
Converting back and related converters
To go from inches to millimeters, multiply by 25.4. The Inches to CM Converter gives centimeters, and the Unit Converter can convert inches to millimeters directly. For any other pair of units, open the Unit Converter, or browse every unit converter.
- CM to Inches Converter: the same conversion in the larger metric unit.
- Inches to CM Converter: to convert inches into centimeters instead.
Frequently asked questions
How many inches are in 1 mm?
1 mm = 0.0393700787402 in. The figure does not end, so it is rounded when written out in decimals.
How many mm are in an inch?
Exactly 25.4 millimeters. That is the international definition of the inch.
Is converting mm to inches different from cm to inches?
Only by a factor of ten. Ten millimeters make one centimeter, so dividing millimeters by 25.4 gives the same answer as dividing the equivalent centimeters by 2.54. The CM to Inches Converter covers the larger unit.
How do I convert mm to inches by hand?
Divide by 25.4. For 50 mm, 50 / 25.4 gives 1.96850393701 in. Dividing by 25 instead is a rough shortcut that makes the answer about 1.6 percent too high.