Millimeters to Inches Converter
1 millimeter = 0.03937 inches
Whether you are working in construction or travel, converting from millimeters to inches is a task you will encounter regularly. The millimeter entered common use alongside the metric system in the early 19th century. For quick reference, 1 mm equals 0.0393701 in.
Did you know? Did you know? The millimeter entered common use alongside the metric system in the early 19th century. Meanwhile, the inch was historically defined as the width of a man's thumb. These different origins explain why both units remain in common use today.
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 | 0.03937 |
| 3 | 0.11811 |
| 5 | 0.19685 |
| 10 | 0.3937 |
| 12.7 | 0.5 |
| 19.05 | 0.75 |
| 25.4 | 1 |
| 50 | 1.9685 |
| 100 | 3.937 |
| 254 | 10 |
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.