Inches to Mm Converter
Enter a value in inches to convert it to millimeters — 1 in = 25.4 mm.
Reviewed by the ToolNestr Editorial Team — July 2026
How to convert inches to millimeters
Converting inches to millimeters is a simple multiplication: take your length in inches and multiply by the fixed conversion factor of 25.4 to get millimeters. Because the factor never changes, the same calculation works for any value, from tiny amounts to very large ones. The converter above applies it the moment you type, with no rounding errors in the underlying maths.
Convert imperial drawings and hardware sizes into the millimeters used in metric workshops. Knowing how to move between inches and millimeters is useful whenever measurements are given in one system but you need them in the other — for shopping, travel, study, cooking, engineering or simply comparing figures from different countries.
The reference table below lists common inches values already converted to millimeters, so you can read off everyday amounts at a glance without typing. For the opposite direction, use the Mm to Inches Converter, which reverses the calculation exactly.
The formula and a worked example
Formula
mm = in × 25.4
Worked example
To convert 10 inches: 10 × 25.4 = 254 mm. To convert 25 inches: 25 × 25.4 = 635 mm.
Inches to Mm conversion table
| Inches (in) | Millimeters (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 25 | 635 |
| 50 | 1,270 |
| 100 | 2,540 |
| 250 | 6,350 |
| 500 | 12,700 |
| 1,000 | 25,400 |
Values are rounded for display; the converter above keeps full precision.
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Frequently asked questions
How do I convert inches to millimeters?
Multiply the number of inches by 25.4. For example, 10 in × 25.4 = 254 mm. The converter above does this automatically.
How many millimeters are in one inches?
There are 25.4 millimeters in one inches. Multiply by 25.4 for any amount.
Is this Inches to Mm converter accurate?
Yes. It uses the exact conversion factor of 25.4, so results are precise. Values shown in the table are rounded for readability.
How do I convert millimeters back to inches?
Use our Mm to Inches Converter for the reverse direction, or divide the millimeters value by 25.4.