Inches to Millimeters
Convert inches to millimeters instantly. Change the amount or check the formula below.
More actions
Multiply in by 25.4 to get mm.
Same value in other units View equivalents
| Unit | Equivalent value |
|---|---|
| Meters (m) | 0.127 m |
| Feet (ft) | 0.416667 ft |
| Centimeters (cm) | 12.7 cm |
| Millimeters (mm) | 127 mm |
| Kilometers (km) | 0.000127 km |
How to convert in to mm
Multiply in by 25.4 to get mm.
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Quick reference table
Choose a value below to try it in the live converter.
| Inches | Millimeters |
|---|---|
| 25.4 mm | |
| 50.8 mm | |
| 127 mm | |
| 254 mm | |
| 635 mm | |
| 1,270 mm | |
| 2,540 mm |
Results use the length dimension. Choose compatible units only; the precision selector changes display rounding, not the underlying factor.
Verify in to mm
Using the stated definitions, 1 in = 25.4 mm and 10 in = 254 mm. The live converter accepts your own value; the table provides additional check points.
Conversion method
Multiply in by 25.4 to get mm.
International foot and inch definitions
The international inch is exactly 0.0254 meter and the international foot is exactly 0.3048 meter. For construction plans or survey data, verify which foot standard the source uses.
Length measurements are one-dimensional. Do not reuse a length factor for square feet or cubic feet: those units require squared or cubed factors.
Reference: NIST conversion factors. Calculation and display rounding are separate. See how we calculate.
Fractional inches to metric lengths
Inch ruler marks are exact fractions, not decimal-looking measurements.
| Inches on a ruler | Millimeters | Centimeters |
|---|---|---|
| 1/16 in | 1.5875 mm | 0.15875 cm |
| 1/8 in | 3.175 mm | 0.3175 cm |
| 1/4 in | 6.35 mm | 0.635 cm |
| 1/2 in | 12.7 mm | 1.27 cm |
| 1 in | 25.4 mm | 2.54 cm |
One international inch is exactly 25.4 mm. A fraction such as 1/8 inch is 0.125 inch, not 0.8 inch.
Practical questions: inches to millimeters
How many millimeters is one sixteenth of an inch?
1/16 in = 1.5875 mm. A sixteenth is a fraction, not a decimal digit.
Is 1/16 inch the same as 0.16 inch?
No. 0.16 in = 4.064 mm; by comparison 1/16 in is 1.5875 mm. Read fractional ruler marks as divisions, not decimal hundredths.
Need another compatible unit? convert inches to centimeters. Check definitions and rounding.
Methodology: fixed SI definitions and standards-based factors. For safety-critical use, verify the required industry specification. Check definitions, conventions and sources.