PCB Trace Width Calculator

Minimum copper width for a given current, using the IPC-2221 curve fit. Enter your current and how much temperature rise you are willing to accept, and it returns the width in mils and millimetres.

Minimum trace width 0.300 mm 11.8 mil

How it works

IPC-2221 gives a curve fit relating current, temperature rise and the cross-sectional area of the conductor:

A = ( I / (k × ΔT0.44) )1/0.725

laminatewidth — what you solve forthickness1 oz ≈ 35 µm cross-sectional area = width × thickness — heavier copper needs less width
The formula solves for area; width is what is left once copper thickness is fixed.

A is the area in square mils, I the current in amps and ΔT the rise above ambient. The constant k is 0.048 for an external layer and 0.024 for an internal one — a buried trace cannot shed heat as easily, so it needs roughly twice the copper for the same rise. Width is then area divided by copper thickness, where 1 oz of copper is 1.378 mil.

Reading the result sensibly

  • This is a minimum for heating, not a recommendation. Voltage drop, mechanical robustness and manufacturability often argue for something wider.
  • A 10 °C rise is a common default. 20 °C is acceptable in many designs; 40 °C is aggressive and assumes you know the surrounding thermal picture.
  • The fit assumes still air and a trace of reasonable length. A short link between two pads behaves better than a long run; a trace under a hot component behaves worse.
  • It says nothing about current surges. Inrush and fault currents need separate thought.

Whatever width you settle on, it also has to be one your fabricator can etch. The limits we build to are on the manufacturing capabilities page, and a board uploaded on the order page is measured against them automatically.