Copper Current & Trace Width Calculator
Required trace width for a given current and temperature rise, on external and internal layers, using the IPC-2221 charts — plus the reverse calculation for a trace width you already have.
Where the 10 °C convention comes from
The IPC charts are drawn for a specified temperature rise above ambient, and 10 °C is the usual default for general-purpose boards. It is not a safety limit. A 10 °C rise inside an enclosure that is already 60 °C gives a 70 °C trace, which derates the laminate and softens solder joints over time. For power electronics, motor drives, LED drivers and anything potted or enclosed, size for 5 – 10 °C rise, not 20 – 30 °C, and check the final figure against a thermal image of a real board rather than a chart.
Heavy copper is a different process
Above about 4 oz the fabrication changes. Etching a thick copper layer without undercut needs a different etch process, and any layer that has to carry 10 – 13 oz typically needs either a step-etch or copper fill on the inner layers to keep the dielectric thickness in range. We fabricate finished copper from 1 to 13 oz, with outer base copper up to 18 oz — see capabilities for the process window. If your design needs more than 13 oz finished, that is a copper bar or busbar problem, not a PCB problem.