Millimeter to Inch Converter
Converts millimeter to inch (mm to in) and back. The conversion factor is shown below every result.
How to Convert Millimeter to Inch
What Is a Millimeter?
A millimeter (mm) is an SI unit of length equal to one thousandth of a meter.
What Is an Inch?
The inch (in), used in both US customary and imperial systems, is fixed at exactly 25.4 millimeters.
Common Millimeter to Inch Reference Points
Real-world reference values for quick sanity checks.
| Item | Millimeter (mm) | Inch (approx.) |
|---|---|---|
| A US quarter's diameter | 24.26 mm | 0.955 in |
| A credit card's thickness | 0.76 mm | 0.030 in |
| 1 inch | 25.4 mm | 1 in |
| Reference values are illustrative approximations for common items, not measured specifications. | ||
Millimeter to Inch Conversion Table
| Millimeter (mm) | Inch (in) |
|---|---|
| 1 mm | 0.03937 in |
| 5 mm | 0.19685 in |
| 10 mm | 0.393701 in |
| 20 mm | 0.787402 in |
| 30 mm | 1.181102 in |
| 50 mm | 1.968504 in |
| 75 mm | 2.952756 in |
| 100 mm | 3.937008 in |
| 150 mm | 5.905512 in |
| 200 mm | 7.874016 in |
| Source: NIST SP 811, Appendix B (1 in = 25.4 mm exactly) | |
Frequently Asked Questions
How do I convert millimeters to inches?
Multiply the millimeter value by 0.0393700787. For example, 25 mm × 0.0393700787 = 0.984251969 in, just under 1 inch.
How many millimeters are in an inch?
Exactly 25.4 millimeters make one inch, per the 1959 International Yard and Pound Agreement.
Why do some tools show measurements in both mm and inches?
Electronics, machining, and photography equipment often display both because component tolerances are frequently specified in millimeters internationally, while many US-made tools and fasteners still use inch-based sizing.
Related Length Converters
A good measuring tool marked in both mm and in removes the guesswork at the point of use.