Electronics · Free Calculator
PCB Trace Resistance Calculator
Find the resistance of a copper PCB track, the voltage drop at a given current and the power lost as heat.
Copper resistanceVoltage dropTemperature effectPower loss
°C
A
Resistance99.11 mΩ
Voltage drop99.11 mV
Power loss99.11 mW
Resistance per cm9.911 mΩ/cm
How this result was calculated
- R = ρ × L ÷ (W × t) × (1 + α (T − 20)) with ρ = 1.724 × 10⁻⁸ Ω·m, α = 0.00393 /°C
- R = 99.11 mΩ, V = I × R = 99.11 mV
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Trace Resistance Formula
R = ρ × L ÷ (W × t) × [1 + α × (T − 20 °C)]
ρ = 1.724 × 10⁻⁸ Ω·m for annealed copper at 20 °C, α = 0.00393 per °C, t = 34.8 µm per oz of copper.
Worked example
A 0.5 mm wide, 100 mm long, 1 oz track at 20 °C: R = 1.724 × 10⁻⁸ × 0.1 ÷ (0.5 × 10⁻³ × 34.8 × 10⁻⁶) = 99 mΩ, so 1 A drops 99 mV.
Key insight: a long thin ground track can easily drop tens of millivolts, which looks like a sensor error on a 4 to 20 mA or bridge input; use a ground plane or star ground.
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Frequently Asked Questions
What is the resistance of 1 oz copper?
About 0.5 mΩ per square at 20 °C. A track 1 mm wide and 1 m long is about 0.5 Ω.
How does temperature affect trace resistance?
Copper resistance rises about 0.39 % per °C.
How can I reduce trace resistance?
Make the track wider, use thicker copper, or run it in parallel on two layers with vias.
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