Inches to mm●
Inches in. Millimetres out. Convert parts and screen sizes in a moment.
Length
Use a decimal point (2.54), scientific notation (1e3), or feet + inches (5 ft 11 in).
Feet + inches detected. The source unit is set to feet. Swap converts the value to the other unit.
Fractional results are rounded to the nearest 1/16 inch.
Try a value
Pick an example to startThe formula
millimetres = inches × 25.4
Multiply the number of inches by 25.4 to get millimetres. To go the other way, divide by the same number.
A worked example
For 2 in, multiply 2 by 25.4. The result is approximately 50.8 mm.
2 × 25.4 ≈ 50.8 mm
Quick reference
Reference values are rounded to 6 decimal places. Use the converter above for other values or precision.
| Inches (in) | Millimetres (mm) |
|---|---|
| 0.125 | 3.175 |
| 0.25 | 6.35 |
| 0.5 | 12.7 |
| 1 | 25.4 |
| 2 | 50.8 |
| 4 | 101.6 |
| 6 | 152.4 |
| 12 | 304.8 |
| 24 | 609.6 |
All equivalent units
The same value, in every supported unit.
Length conversions
For parts, screws and screen sizes.
Use this conversion for bolt and pipe sizes, drill bits, screen diagonals and drawings that mix metric and imperial. One inch is exactly 25.4 millimetres, so multiply by 25 and add a little for a quick estimate.
Calculation details & precision
Length conversions use metres as the base unit. The international inch is exactly 0.0254 m; a foot is 12 inches, an international mile is 1,609.344 m, and an international nautical mile is 1,852 m.
Automatic displays up to 12 significant digits. Choose 2, 4 or 6 decimal places in Precision for a shorter result. Displayed results are rounded; very large or small values use scientific notation.
Common questions
Is an inch exactly 25.4 mm?
Yes. Since 1959 the international inch has been defined as exactly 25.4 millimetres.
How many millimetres are in 1 inches?
1 in is approximately 25.4 mm. The converter can show more significant digits or round to a chosen number of decimal places.