PCB calculators / Layout & fabrication
Free tool · PreBuild Engineering
PCB trace resistance and voltage drop calculator
Check how many millivolts your power and ground traces lose before the load sees them.
Inputs
mm
mm
A
°C
V
Result
—
Why it matters
A few tens of milliohms is invisible on a schematic but becomes hundreds of millivolts at load currents, enough to brown out a microcontroller or shift an ADC reference. The return path counts too.
Formula
R = ρ(T) · L / (w · t)
ρ(T) = 1.724×10⁻⁸ Ω·m × (1 + 0.00393 × (T − 20 °C))
t = 34.8 µm per oz of copper
Design tips
- Copper resistance rises about 0.4% per °C: hot traces drop more.
- Finished outer-layer copper is often thicker than the base foil after plating; inner layers usually are not.
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.