Required copper trace width for a target current and temperature rise, per IPC-2221.

How IPC-2221 sizes a trace

The current a copper trace can carry is limited by self-heating. IPC-2221 fits the allowed cross-sectional area to the current and the temperature rise you accept:

A = (\frac{I}{k Δ T ^{0.44}})^{1/0.725}

with $A$ in mils², $I$ in amperes and $Δ T$ in °C. The constant $k = 0.048$ for external layers and $k = 0.024$ for internal layers, which trap heat and so need roughly twice the copper. Width then follows from the copper thickness:

W = \frac{A}{t} t = 1.378 mils \times oz

One ounce of copper is 35 µm (1.378 mils) thick. Keep ΔT conservative (10–20 °C) for signal and supply traces; high-power planes can tolerate more. These are minimums — widen for margin, vias and connector pads.

PCB Trace Width Calculator

How IPC-2221 sizes a trace