PCB Trace Width Calculator
Boards fail at the traces nobody sized. This is the IPC-2221 nominal curve the fab calculators use: current, copper weight and allowed temperature rise in, minimum trace width out, in mils and millimetres.
Result
A = (I / (k × ΔT^0.44))^(1/0.725) = 16.3 mil² → width = A / 1.38 mil = 11.8 mil
| Quantity | Value |
|---|---|
| Minimum width | 11.8 mil = 0.3 mm |
| Resistance | 16.5 mΩ/cm, 82.3 mΩ over 50 mm |
| Voltage drop | 0.0823 V at 1 A |
| Power in the trace | 0.0823 W |
| Verdict | On the IPC-2221 nominal curve for a 10°C rise, an external trace at 1 A wants at least 11.8 mil (0.3 mm) of 1 oz copper. Add margin for long runs, and remember vias and connectors carry the same current. |
The curve assumes still air at room temperature and a single trace. Bundled traces, enclosed cases, altitude and continuous duty all argue for going wider; the same current in a via needs its own check (a 0.3 mm via barrel is about 1 A).
FAQ
External or internal layer?
External traces sit in air and cool better, so the curve allows roughly double the current of an internal layer at the same width. When a design error forces a change, this is usually where it hides.
What about peaks and inrush?
The curve describes steady state. Motor inrush or a capacitor bank charging can be ten times the running current for milliseconds; size for the peak if it repeats, and let the copper absorb one-off surges.
How much margin is enough?
Ten to twenty percent of width on top of the curve is cheap insurance, and fab tolerance eats a little of every trace anyway. On power paths, prefer wider copper and thicker plating over trusting the minimum.
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