UnitConMillimeters to Inches Converter
Convert millimeters to inches for fastener sizes, drill bits, pipe diameters, and consumer product specifications. This is a critical conversion for mechanics and engineers working across metric and imperial standards.
Formula
Divide millimeters by 25.4 to get inches. To reverse, multiply inches by 25.4 to get millimeters.
Quick reference
| Millimeter (mm) | Inch (in) |
|---|---|
| 1 | 0.03937008 |
| 2 | 0.07874016 |
| 3 | 0.1181102 |
| 5 | 0.1968504 |
| 6 | 0.2362205 |
| 10 | 0.3937008 |
| 12 | 0.4724409 |
| 15 | 0.5905512 |
| 20 | 0.7874016 |
| 25 | 0.984252 |
About these units
Millimeter
The millimeter has been part of the metric system since its introduction in France in the late 18th century. Its precise definition as 0.001 meters makes it ideal for engineering applications where decimal fractions of a meter are impractical.
Inch
The inch is defined as exactly 25.4 mm under the 1959 international agreement. In engineering, fractional inches (1/4, 1/8, 1/16) remain common in the US, making mm-to-inch conversions a daily necessity in many workshops.
Frequently asked questions
10 ÷ 25.4 ≈ 0.394 inches, or just under 3/8 inch.
3/8 × 25.4 = 9.525 mm.
25 ÷ 25.4 ≈ 0.984 inches — just under 1 inch.