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How to Convert Inches to Millimeters
Multiply the inch value by 25.4. This conversion factor is exact, as one inch is internationally defined as 25.4 mm.
Inches to Millimeters Conversion Table
| Inches | Millimeters |
|---|---|
| 0.5 | 12.7 |
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 15 | 381 |
| 20 | 508 |
| 25 | 635 |
| 50 | 1270 |
| 100 | 2540 |
| 250 | 6350 |
| 500 | 12700 |
| 1000 | 25400 |
How Many Millimeters in a Inche?
1 inche equals 25.4 millimeters. To convert any value, multiply the number of inches by 25.4.
Common Use Cases
Plumbers working with copper and PEX tubing encounter pipe sizes described in inches (such as 1/2 inch or 3/4 inch) but need millimeter equivalents when ordering metric fittings or working with imported fixtures. A 1/2-inch pipe has an outer diameter of 12.7 mm, and selecting the correct compression ring or solder fitting depends on this precise conversion.
Electronics hobbyists designing printed circuit boards (PCBs) in imperial-grid software often need to convert pad sizes and trace widths to millimeters for metric component datasheets. A 0.1-inch pin pitch is 2.54 mm, and this conversion is so fundamental to PCB design that the number 2.54 is practically memorized by anyone who regularly lays out boards.
Automotive mechanics working on imported vehicles may find bolt and fastener specifications listed in inches in a US repair manual, while the actual hardware is metric. Converting a 5/16-inch bolt (7.9375 mm) to its nearest metric equivalent (8 mm) helps identify the correct socket and replacement fastener without trial-and-error fitting.