Free tool
Trace width calculator
How wide does a track have to be to carry a current without cooking? IPC-2221 is the estimate the industry sizes copper with, and this calculator uses the same function Amptrace runs across every segment of a real board.
What width do I need?
0.781 mm (31 mil)
An inner layer needs roughly twice the copper for the same rise: it is surrounded by laminate and has nowhere to put the heat.
What will this width do?
The question you have when the board already exists. Same current, same copper, same layer as on the left.
+65 K
Over ambient, in still air, with nothing else nearby. A rise of 10–20 K is the usual budget; above about 40 K most people go back and widen the track.
What this calculator cannot see
IPC-2221 sizes one isolated trace in still air. It is a good estimate, which is why it is used everywhere, but it does not know four things that turn up on a real board:
- Where the current actually goes. The number above assumes you already know the current in this track. On a real board that is the hard part: a rail that splits four ways, a return that takes the low-impedance path instead of the one you drew, a plane carrying most of it.
- Its neighbours. Two 2 A tracks side by side are hotter than one, and this formula treats each as if it were alone.
- The copper around it. A track leaving a pour sheds heat into it; the same track crossing a gap does not.
- Vias. A 2 A track that necks down to one via has its narrowest point somewhere no width calculator was ever pointed at.
Amptrace meshes the copper you drew, solves the current in every segment and via, and then applies this same check to each of them, so you get an answer for every track. How the solve works, or what else it checks.
The formula
IPC-2221 relates current to cross-section and temperature rise as I = k · ΔT^0.44 · A^0.725, with A in square mils and k at 0.048 for an outer layer and 0.024 for an inner one. Solving it for area gives the width above. Both directions are the same two functions the board check calls, and a test asserts that the two agree across every combination on this page.