PCB trace resistance & current calculator
Interactive engineering and procurement calculator. Instant client-side computation with no sign-up.
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Results
Trace resistance (R)
ρ × L ÷ (W × t), ρ(Cu) = 1.724e-8 Ω·m
Voltage drop (V)
I × R
Copper loss (P)
I² × R — heats the board
About the model
Resistance comes from R = ρ·L/A: copper resistivity ρ ≈ 1.724e-8 Ω·m at 20 °C, length in metres, cross-section in m² (width in mil × copper thickness). A 1 oz layer is ≈ 35 µm thick, and 1 mil = 0.0254 mm. The IPC-2221 width formula I = k·ΔT^0.44·A^0.725 uses area in mil² and k = 0.048 for external traces — internal traces dissipate heat about half as well, so k drops to 0.024 and the trace must be wider for the same current. Resistivity rises with temperature (~0.4%/°C), and vias, connectors and solder add resistance the model ignores — treat results as estimates.
Designers also reach for PCB connectors and terminal blocks where the trace meets the outside world.
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