PCB Trace Width Calculator (IPC-2221)
Find the copper trace width you need for a given current and temperature rise. Add the trace length to get its resistance and voltage drop too.
Formula and cautions
The IPC-2221 relation I = k·ΔT^0.44·A^0.725 is solved for the cross-section A in mil², then divided by the copper thickness to get the width. k is 0.048 for outer layers and 0.024 for inner layers. Inner layers shed heat poorly, so they need more than twice the width for the same current. The formula is conservative, which makes it a safe design starting point.
Frequently asked questions
How wide should a trace be for 1 A?
With 1 oz copper on an outer layer and a 10 °C rise, IPC-2221 gives about 0.3 mm (12 mil). An inner layer needs about 0.8 mm for the same current.
Does thicker copper help?
Yes. 2 oz copper is twice as thick, so the same current needs roughly half the width. It costs more and makes fine-pitch routing harder.