CloudCalcAppInches to Millimeters Converter
Convert inches to millimeters instantly. 1 inch equals exactly 25.4 millimeters - enter a length in inches below to get the equivalent in millimeters, useful for precision parts, tools, and technical drawings.
Quick answer
Formula
millimeters = inches × 25.4
Quick mental-math estimate
Worked Example: Convert 0.5 Inches to Millimeters
- Given1 inch = 25.4 millimeters, exactly.
- Formulamillimeters = inches × 25.4
- Substitutemillimeters = 0.5 × 25.4
- Answer0.5 inches = 12.7 millimeters.
Quick Examples
1 in = 25.4 mm
1 in = 25.4 mm - the exact definition this converter uses.
2 in = 50.8 mm
2 in = 50.8 mm.
5 in = 127 mm
5 in = 127 mm.
10 in = 254 mm
10 in = 254 mm.
12 in = 304.8 mm
12 in = 304.8 mm - exactly 1 foot.
20 in = 508 mm
20 in = 508 mm.
Conversion Table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 5 | 127 |
| 6 | 152.4 |
| 7 | 177.8 |
| 8 | 203.2 |
| 9 | 228.6 |
| 10 | 254 |
| 12 | 304.8 |
| 15 | 381 |
| 20 | 508 |
Common Inch Fractions in Millimeters
Each fraction below converts to an exact millimeter value (fraction × 25.4) - these are precise conversions, not approximations.
| Fraction | Inches (in) | Millimeters (mm) |
|---|---|---|
| 1/16 in | 0.0625 | 1.5875 |
| 1/8 in | 0.125 | 3.175 |
| 3/16 in | 0.1875 | 4.7625 |
| 1/4 in | 0.25 | 6.35 |
| 3/8 in | 0.375 | 9.525 |
| 1/2 in | 0.5 | 12.7 |
| 5/8 in | 0.625 | 15.875 |
| 3/4 in | 0.75 | 19.05 |
| 7/8 in | 0.875 | 22.225 |
| 1 in | 1 | 25.4 |
Unit Definitions
Inches (in)
A US customary and imperial unit equal to exactly 2.54 centimeters.
imperial system
- Screen and display sizes
- Woodworking and construction
- Paper sizes and printing
Millimeters (mm)
One thousandth of a meter - the smallest metric length unit in common everyday use.
metric system
- Machining and engineering tolerances
- Paper and material thickness
- Rainfall measurement
FAQ
How do you convert inches to millimeters?
Multiply the length in inches by 25.4. For example, 5 inches × 25.4 = 127 millimeters.
How many millimeters are in 1 inch?
1 inch equals exactly 25.4 millimeters.
How many millimeters is 1/4 inch?
1/4 inch equals exactly 6.35 millimeters (0.25 × 25.4) - see the Common Inch Fractions reference below for other frequently used fraction sizes.
Is 1 inch exactly 25.4 mm?
Yes. The international inch has been defined as exactly 25.4 millimeters since 1959, so this conversion is exact, not a rounded approximation.
When is inch-to-millimeter conversion useful?
It's commonly needed when a US/imperial measurement (a tool, a part, a drawing dimension) must be matched against millimeter-based specifications used in most manufacturing and engineering contexts worldwide.
Displayed results are rounded to a maximum of 4 decimal places for readability (extended only in the rare case a nonzero value would otherwise display as “0”), and whole-number results are shown without unnecessary decimals. The conversion factor and formula above are the exact relationship - only the calculator's displayed output is rounded.
Need a different unit? Length Converter supports many other unit conversions.