PCB trace width calculator

IPC-2221 is a curve fit to measurements from 1954-era charts, not first-principles physics: it assumes a single DC current in a long straight trace with copper at room temperature plus your rise, and it carries no derating for vias, parallel traces, component pads, or enclosed boards. IPC-2152 replaced it in 2009 and is the standard to reach for when the run matters, but IPC-2221 with a margin remains common practice for sizing. Resistance here uses the width the run actually carries, the minimum when you have not planned one, at copper's resistivity evaluated at 20 C plus your rise.