Formula: mm = mil × 0.0254 · mil = mm ÷ 0.0254
Mil to mm conversion table
Common trace widths, clearances, and pad dimensions used in PCB layout.
| Mils (mil) | Millimeters (mm) | Typical use |
|---|---|---|
| 1 | 0.0254 | — |
| 4 | 0.1016 | Fine-pitch clearance |
| 5 | 0.127 | Min trace (advanced) |
| 6 | 0.1524 | Dense-board clearance |
| 8 | 0.2032 | Common trace width |
| 10 | 0.254 | Standard trace width |
| 12 | 0.3048 | Signal trace |
| 15 | 0.381 | — |
| 20 | 0.508 | Power trace |
| 25 | 0.635 | — |
| 30 | 0.762 | — |
| 40 | 1.016 | — |
| 50 | 1.27 | Wide power trace |
| 100 | 2.54 | Pad / via spacing |
| 200 | 5.08 | — |
How to convert mils to mm
A mil (also called a "thou") is one thousandth of an inch — 0.001 in. Because one inch is exactly 25.4 mm, a single mil equals 0.0254 mm. To convert any measurement, multiply the number of mils by 0.0254:
mils = millimeters ÷ 0.0254
For example, a 10 mil trace is 0.254 mm wide — a typical minimum for standard PCB fabrication. A 6 mil clearance works out to 0.1524 mm, common on denser boards.
Why mils matter in PCB design
Most PCB CAD tools default to mils for trace widths, spacing, drill sizes, and pad geometry, while fabrication houses often quote capabilities in millimeters. Mixing the two units is one of the most common sources of manufacturing errors — a quick, reliable conversion keeps your design rules and your fab's tolerances in sync.
Frequently asked questions
- How many mm is 10 mil?
- 10 mil equals 0.254 mm — a common minimum trace width in standard PCB fabrication.
- Is a mil the same as a millimeter?
- No. A mil is 0.001 inch (0.0254 mm), while a millimeter is 0.001 meter. One mm is about 39.37 mils.
- What is 1 mil in mm?
- 1 mil is exactly 0.0254 mm.
Skip the unit math entirely
IntelCAD.ai handles design rules, trace widths, and clearances for you — describe the board, and the AI routes a production-ready PCB.
Launch the Demo