Millimeters to Inches Converter
1 millimeter = 0.03937 inches
Conversion formula
inches = millimeters / 25.4
To convert millimeters to inches, divide by 25.4. Since 1 inch is exactly 25.4 mm, the conversion is straightforward and exact.
Millimeters to Inches Table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.0393701 |
| 3 | 0.11811 |
| 5 | 0.19685 |
| 10 | 0.393701 |
| 12.7 | 0.5 |
| 19.05 | 0.75 |
| 25.4 | 1 |
| 50 | 1.9685 |
| 100 | 3.93701 |
| 254 | 10 |
1 millimeter in every length unit
| Meters | 0.001 m |
| Kilometers | 0.000001 km |
| Centimeters | 0.1 cm |
| Micrometers | 1,000 um |
| Nanometers | 1,000,000 nm |
| Miles | 6.21371e-7 mi |
| Yards | 0.00109361 yd |
| Feet | 0.00328084 ft |
| Inches | 0.0393701 in |
| Nautical Miles | 5.39957e-7 nmi |
| Light Years | 1.057e-19 ly |
About Millimeters to Inches
The millimeters-to-inches conversion is crucial in engineering, manufacturing, 3D printing, and hardware selection where precision matters down to fractions of an inch.
Socket and wrench sizes are a prime example. A 10 mm socket is 0.394 inches - close to but not exactly 3/8 inch (9.525 mm). A 13 mm wrench is about 0.512 inches, nearest to 1/2 inch. This is why mixing metric and SAE tools can strip bolt heads.
In 3D printing and CNC machining, nozzle sizes are typically in mm: a 0.4 mm nozzle is about 0.0157 inches. Layer heights of 0.2 mm equal 0.00787 inches.
Paper thickness is measured in mm: standard copy paper is about 0.1 mm (0.00394 inches) thick. Cardstock ranges from 0.3 to 0.5 mm (0.012 to 0.02 inches).
Rainfall measurements often convert between systems too. A 25 mm rainfall is approximately 1 inch, which weather services consider significant.
For jewelry, ring band widths commonly range from 2 mm (thin, about 5/64 inch) to 8 mm (wide, about 5/16 inch). Gemstone sizes in mm are matched to inch-based settings.
A handy reference: 25.4 mm = 1 inch exactly. So 50 mm is about 2 inches, and 100 mm is approximately 4 inches.
Frequently Asked Questions
How many mm in 1 inch?
There are exactly 25.4 millimeters in 1 inch. This is a precise, internationally agreed-upon definition.
What is 10 mm in inches?
10 mm equals 0.3937 inches, which is close to but not exactly 3/8 inch (0.375 inches or 9.525 mm).
How do I convert mm to fractional inches?
Divide mm by 25.4 to get decimal inches, then convert to the nearest fraction. For example, 6.35 mm / 25.4 = 0.25 inches = 1/4 inch.
Can I use metric and SAE tools interchangeably?
Not reliably. While some sizes are close (10 mm and 3/8", 19 mm and 3/4"), the slight differences can round off bolt heads. Always use the correct system for your fastener.