Millimeters to Inches Converter
Convert millimeters to inches and back. 1 millimeter = 0.0393700787402 inches (rounded).
Tip: Results show up to 8 significant digits. The factors and their sources are listed on the "Where our numbers come from" page.
On this page
Millimeters and Inches
One millimeter is about 0.0393700787402 inches, and one inch is exactly 25.4 millimeters. The converter works both ways: use the two tabs at the top of the tool to choose the direction.
Quick conversion table
Millimeters to Inches
| Millimeters | Inches |
|---|---|
| 1 mm | 0.039370079 in |
| 2 mm | 0.078740157 in |
| 5 mm | 0.19685039 in |
| 6 mm | 0.23622047 in |
| 8 mm | 0.31496063 in |
| 10 mm | 0.39370079 in |
| 12 mm | 0.47244094 in |
| 15 mm | 0.59055118 in |
| 20 mm | 0.78740157 in |
| 25.4 mm | 1 in |
| 50 mm | 1.9685039 in |
| 100 mm | 3.9370079 in |
| 1,000 mm | 39.370079 in |
Inches to Millimeters
| Inches | Millimeters |
|---|---|
| 0.0625 in | 1.5875 mm |
| 0.125 in | 3.175 mm |
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 6 in | 152.4 mm |
| 12 in | 304.8 mm |
| 24 in | 609.6 mm |
| 36 in | 914.4 mm |
Exact factor and source
| Conversion | Value | Basis |
|---|---|---|
| 1 millimeter in inches | 0.0393700787402 | rounded to 12 digits. SI Brochure, 9th edition (BIPM 2019): SI prefix milli = 10^-3 |
| 1 inch in millimeters | 25.4 | exact. NIST SP 811 (2008), Appendix B.8: 1 in = 0.0254 m, exact by the 1959 international yard and pound agreement |
How to convert millimeters to inches
- Step oneTake the number of millimeters.
- Step twoMultiply it by 0.0393700787402.
- Step threeThe result is the number of inches.
- Step fourTo go back, divide by 0.0393700787402, or multiply by 25.4.
Example: 100 mm x 0.0393700787402 = 3.93700787402 in.
All length units compared
Each unit written in meters, the base unit of this tool. Exact values come straight from the definitions.
| Unit | Symbol | Value in meters |
|---|---|---|
| Millimeters | mm | 0.001 meters |
| Centimeters | cm | 0.01 meters |
| Meters | m | 1 meter |
| Kilometers | km | 1,000 meters |
| Inches | in | 0.0254 meters |
| Feet | ft | 0.3048 meters |
| Yards | yd | 0.9144 meters |
| Miles | mi | 1,609.344 meters |
What is a millimeter?
The millimeter (mm) is one thousandth of a meter (0.001 m). It is used for small measurements such as screw sizes, paper thickness and camera lenses.
What is an inch?
The inch (in) is a US customary unit of length, exactly 2.54 centimeters by international agreement. 12 inches make a foot.
What this converter does not do
- Results are rounded for display to 8 significant digits; the stored factor is the exact one.
- It uses the international foot (exactly 0.3048 m), not the older US survey foot.
- It converts lengths only; it does not convert between a length and a time, a pace or an area.
Frequently asked questions
How many inches are in a millimeter?
1 millimeter is about 0.0393700787402 inches. The factor is rounded to 12 significant digits.
How many millimeters are in an inch?
1 inch is exactly 25.4 millimeters.
How many inches is 100 mm?
100 mm is 3.9370079 inches, or 10 centimeters.
Where do the factors come from?
Millimeters: SI Brochure, 9th edition (BIPM 2019): SI prefix milli = 10^-3. Inches: NIST SP 811 (2008), Appendix B.8: 1 in = 0.0254 m, exact by the 1959 international yard and pound agreement.
References
- Millimeters: SI Brochure, 9th edition (BIPM 2019): SI prefix milli = 10^-3
- Inches: NIST SP 811 (2008), Appendix B.8: 1 in = 0.0254 m, exact by the 1959 international yard and pound agreement
- NIST Special Publication 811: Guide for the Use of the International System of Units (SI), 2008 edition.
- The International System of Units (SI Brochure), 9th edition, BIPM.