PCB calculators / Layout & fabrication
Free tool · PreBuild Engineering
PCB trace width calculator
Find the minimum copper width that carries your current without overheating, for outer and inner layers.
Inputs
A
°C
mm
°C
Result
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Why it matters
An undersized trace heats up, raises resistance and drops voltage under load. In the worst cases it delaminates or fuses. Inner layers cool worse than outer layers, so they need roughly 2.6× the width for the same current.
Formula
A = ( I / (k · ΔT^0.44) )^(1/0.725) [A in mil², I in A, ΔT in °C]
k = 0.048 external, 0.024 internal
Width = A / (1.378 mil × copper oz)
Design tips
- Size power traces for peak, not average, current when pulses last longer than a few seconds.
- Planes and pours carry current far better than traces: use them for anything above a few amps.
- Check connector pins and vias too: they are often the real bottleneck.
Results are engineering estimates from standard formulas and published approximations. Always confirm against component datasheets, your fabricator's capabilities and, for critical designs, simulation or measurement.