Length conversion
Inches to Millimetres (in to mm)
1 in = 25.4 mm — multiply the number of inches by 25.4.
Inches to Millimetres conversion chart
| inches | millimetres |
|---|---|
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 5 in | 127 mm |
| 6 in | 152.4 mm |
| 7 in | 177.8 mm |
| 8 in | 203.2 mm |
| 9 in | 228.6 mm |
| 10 in | 254 mm |
| 12 in | 304.8 mm |
| 15 in | 381 mm |
| 18 in | 457.2 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 30 in | 762 mm |
| 40 in | 1016 mm |
| 50 in | 1270 mm |
| 60 in | 1524 mm |
| 75 in | 1905 mm |
| 100 in | 2540 mm |
How to convert by hand
1 in = 25.4 mm
Because this is a linear conversion, the ratio never changes: every inche is always 25.4 mm, whatever the size of the number.
Worked example: 10 in × 25.4 = 254 mm .
Related conversions
About inches and millimetres
Length conversions come up constantly when a product is specified in one system and you think in the other — screen sizes in inches, running distances in kilometres, height in feet.
Inch
US / ImperialDefined as exactly 2.54 centimetres since the 1959 international yard agreement.
Commonly used for: Screen sizes, tyre diameters and US construction.
Millimetre
Metric (SI)One thousandth of a metre.
Commonly used for: Engineering drawings, rainfall totals and material thicknesses.
Questions
How many millimetres are in one inche?
One inche equals 25.4 mm. To convert any amount, multiply the number of inches by 25.4.
What is 5 in in mm?
5 in = 127 mm. Type any value into the converter above to get an exact answer.
How do I convert millimetres back to inches?
Divide by 25.4 instead of multiplying — or use our Millimetres to Inches converter.
Is this converter accurate?
Yes. Linear conversions use the internationally agreed factors published by NIST (SP 811), and temperature conversions use the exact defining formulas. Calculations run at full double precision and are only rounded for display.
Need a different unit?
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