Length conversion
Inch to Millimetre
One inch is 25.4 millimetres. Enter any value below to convert it instantly, or use the reference table further down for the numbers you need most often.
Conversion rate
1 in = 25.4 mm
mm = in × 25.4
1 in = 25.4 mm
Reference
Inch to Millimetre table
The values people look up most often, rounded for practical use.
| Inch (in) | Millimetre (mm) | Written out |
|---|---|---|
| 1 in | 25.4 mm | 1 inches = 25.4 millimetres |
| 2 in | 50.8 mm | 2 inches = 50.8 millimetres |
| 3 in | 76.2 mm | 3 inches = 76.2 millimetres |
| 5 in | 127 mm | 5 inches = 127 millimetres |
| 10 in | 254 mm | 10 inches = 254 millimetres |
| 15 in | 381 mm | 15 inches = 381 millimetres |
| 20 in | 508 mm | 20 inches = 508 millimetres |
| 25 in | 635 mm | 25 inches = 635 millimetres |
| 50 in | 1,270 mm | 50 inches = 1,270 millimetres |
| 100 in | 2,540 mm | 100 inches = 2,540 millimetres |
| 250 in | 6,350 mm | 250 inches = 6,350 millimetres |
| 500 in | 12,700 mm | 500 inches = 12,700 millimetres |
| 1,000 in | 25,400 mm | 1,000 inches = 25,400 millimetres |
How to convert inches to millimetres
Multiply the number of inches by 25.4. That is the whole calculation: mm = in × 25.4. To go back the other way, divide instead, or multiply by 0.03937.
Worked example: 12 inches × 25.4 = 304.8 millimetres.
Where this conversion comes up
Length conversions show up constantly in printing, DIY, engineering drawings and anything bought from a country using the other measurement system. If you are converting in order to set a page or grid size, the graph paper generator accepts spacing in millimetres directly, and the on-screen ruler lets you check a printed result against both scales.
Quick answers
- 1 inch = 25.4 millimetres
- 2 inches = 50.8 millimetres
- 5 inches = 127 millimetres
- 10 inches = 254 millimetres
- 100 inches = 2,540 millimetres
More conversions
Other length conversions
Answers
Frequently asked questions
mm = in × 25.4. The converter above applies it for you, but the formula is useful in a spreadsheet, put your value in column A and the formula in column B.Related tools
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