How to convert millimeters to inches
To convert millimeters to inches, multiply by 0.0393700787402. One inch is exactly 25.4 mm, so this conversion is exact and widely used for tools, hardware, jewelry and engineering drawings.
Millimeter to Inch conversion table
| Millimeter (mm) | Inch (in) |
|---|---|
| 0.1 mm | 0.00393700787402 in |
| 0.5 mm | 0.0196850393701 in |
| 1 mm | 0.0393700787402 in |
| 2 mm | 0.0787401574803 in |
| 3 mm | 0.11811023622 in |
| 4 mm | 0.157480314961 in |
| 5 mm | 0.196850393701 in |
| 10 mm | 0.393700787402 in |
| 20 mm | 0.787401574803 in |
| 25 mm | 0.984251968504 in |
| 50 mm | 1.96850393701 in |
| 100 mm | 3.93700787402 in |
| 500 mm | 19.6850393701 in |
| 1,000 mm | 39.3700787402 in |
About the units
Millimeter (mm)
A millimeter is one thousandth of a meter. It is the standard unit on engineering drawings, rulers and screw sizes.
Inch (in)
An inch is defined as exactly 2.54 centimeters. It is used in the US and UK for screen sizes, lumber and personal height.
How to use this converter
- Type the number of millimeters (mm) in the input box.
- The result in inches appears instantly — no button needed.
- See the same value in every other length unit just below.
- Use “Swap units” to convert inches back to millimeters.
When you’ll use the millimeter to inch conversion
A ring size chart lists an inner diameter of 17.3 mm. Converting gives about 0.68 inches, which helps compare with a US sizing chart.
A camera lens has a 77 mm filter thread and you want the size in inches for an imported filter listing.
💡 For a quick estimate in your head, multiply by about 0.039 (the exact factor is 0.0393700787402).
Watch out for these mix-ups
- Dividing by 25 instead of 25.4.
- Assuming close sizes are interchangeable for bolts and wrenches.
- Rounding precision work too early.
- Reading fractional inch sizes as decimals.
Tips for better results
- Divide millimeters by 25.4.
- Keep three decimal places for precision work.
- Use metric tools on metric fasteners.
💡 Practical tip: A 13 mm wrench is close to ½ inch (12.7 mm) but may round off bolt heads if used interchangeably.
Frequently asked questions
How many inches are in one millimeter?
One millimeter equals 0.0393700787402 inches. 0.0393700787402 is the exact factor used by this converter.
How do I convert millimeters to inches?
Multiply the value in millimeters by 0.0393700787402. To go the other way, multiply inches by 25.4.
What is 10 mm in in?
10 mm = 0.393700787402 in. Also, 5 mm = 0.196850393701 in and 100 mm = 3.93700787402 in.
What is the difference between a millimeter and a inch?
A millimeter is one thousandth of a meter. It is the standard unit on engineering drawings, rulers and screw sizes. An inch is defined as exactly 2.54 centimeters. It is used in the US and UK for screen sizes, lumber and personal height.
Is this tool free and private?
Yes — the Millimeter to Inch is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
Related tools
📬 Get new tools first — free
Join Taurang to hear about new calculators, converters and features. No spam; unsubscribe anytime.