Millimeters to Inches (mm to in) Converter
Instantly convert between millimeters (mm) and inches (in). Enter a value in either field to see the live conversion as both a decimal and a fraction.
How to Convert Millimeters to Inches
Converting from millimeters (mm) to inches (in) is a common task in engineering, manufacturing, and everyday DIY projects. The process is straightforward and relies on a single conversion factor.
The Conversion Formula
The internationally accepted conversion factor is:
Therefore, to convert from millimeters to inches, you simply divide the number of millimeters by 25.4. Alternatively, you can multiply by the reciprocal, 0.0393701.
- Formula 1 (Division): Inches = Millimeters / 25.4
- Formula 2 (Multiplication): Inches = Millimeters × 0.0393701
For example, to convert 10mm to inches:
10 mm / 25.4 = 0.3937... inches
Common MM to Inches Conversion Chart
Here is a quick reference table for common millimeter to inch conversions.
| Millimeters (mm) | Inches (Decimal) | Inches (Fraction) |
|---|---|---|
| 1 mm | 0.039 in | ~ 5/128" |
| 5 mm | 0.197 in | ~ 13/64" |
| 10 mm | 0.394 in | ~ 25/64" |
| 20 mm | 0.787 in | ~ 25/32" |
| 25.4 mm | 1.000 in | 1" |
| 50 mm | 1.969 in | ~ 1 31/32" |
| 100 mm | 3.937 in | ~ 3 15/16" |
Frequently Asked Questions (FAQ)
How many mm are in one inch?
There are exactly **25.4 millimeters (mm)** in one inch (in). This definition was standardized in 1959 as part of the International Yard and Pound Agreement.
Is 10mm half an inch?
No, 10mm is not half an inch. A half-inch is 0.5 inches, which is exactly **12.7 mm**.
10mm is approximately 0.3937 inches, which is slightly more than 3/8" (0.375 in) and just under 13/32" (0.406 in).
How do you read mm to inches on a ruler?
Most standard rulers show inches on one side and centimeters (cm) / millimeters (mm) on the other. 1 centimeter is equal to 10 millimeters. To convert, you can visually compare the measurements. You will see that 2.54 cm (or 25.4 mm) lines up exactly with the 1-inch mark.