PCB Trace Width Calculator (IPC-2221)

IPC-2221 relates the current a copper trace carries to how much it heats up: I = k · ΔT^0.44 · A^0.725, with A the cross-section in square mils and k = 0.048 for outer layers, 0.024 for inner ones. This calculator runs it both ways — the width needed for a current, or the current a given width can take — for any copper weight (0.5 to 4 oz/ft² or a thickness in µm or mil, with 1 oz taken as 1.378 mil = 35 µm) and any allowed rise above ambient. With a trace length it also gives the resistance at the operating temperature (annealed copper, 1.7241 µΩ·cm at 20 °C, rising 0.393 % per °C), the voltage drop and the power the trace dissipates. The classic check: 1 A with a 10 °C rise on 1 oz copper needs 11.8 mil (0.30 mm) on an outer layer and 30.8 mil (0.78 mm) inside the board. Treat the answer as a starting point, not a guarantee. The formula is a curve fitted to measurements from the 1950s on isolated traces in still air, and it knows nothing about copper pours, vias, neighbouring hot parts, board thickness or airflow. It was drawn for up to 35 A, widths up to 400 mil and rises of 10 to 100 °C; beyond that the tool still answers but says so. IPC-2152, which replaced these charts in 2009, found the inner-layer factor far too pessimistic — internal traces usually run cooler than IPC-2221 predicts because the laminate spreads heat — so an inner-layer width from here errs on the safe side. Manufacturing limits such as minimum width, spacing and the plating added to outer layers are separate questions.