PCB Trace Width Calculator
A trace is the copper path that carries current across a printed circuit board. A wider trace carries more current before it heats up. This page estimates the width needed for a given current and temperature rise.
It uses the IPC-2221 formula, which is widely used in the electronics industry.
- Free
- Works offline after your first visit
- Saves on this device
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- Updated
How it works
The method first works out the cross-section a trace needs from the current and the allowed temperature rise. Outer layers shed heat better than inner layers, so the constant is larger for them. That cross-section is divided by the copper thickness, 1.378 mils for 1 ounce copper, to give the width.
The result is a starting estimate. Board makers publish their own rules, and the final choice depends on copper weight, trace length and how the board is built.
Worked example
For 2 amps of current with a 10 degree temperature rise on an outer layer, the trace needs to be about 0.03 in wide.
Questions
Why can an outer trace be narrower for the same current?
Outer copper sits in open air and sheds heat better, so the same temperature rise allows more current. This page uses a larger constant for outer layers for that reason.
Does this assume a copper weight?
Yes, 1 ounce copper. Heavier copper needs a narrower trace for the same current, so confirm the weight with your board maker.
What temperature rise should I use?
That depends on the board and on what sits near the trace. Many designers start with a rise of 10 to 20 degrees Celsius, then check the choice with their board maker.
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