PCB Copper Trace Resistance Calculator

DC Resistance of a PCB Trace

A long, narrow copper trace behaves like a resistor. Resistance grows with length and shrinks with cross-sectional area. At higher operating temperatures, copper resistivity also increases.

Resistance Formula

$$R = \frac{\rho \times L}{W \times T}$$

$R$ is resistance, $\rho$ is resistivity, $L$ is length, $W$ is width, and $T$ is thickness. Copper resistivity at 20 °C is about $1.68 \times 10^{-8}\,\Omega\cdot\text{m}$.

Temperature Coefficient

$$\rho(T) = \rho_{20} \times \left(1 + \alpha (T - 20)\right)$$

For copper, $\alpha \approx 0.00393$ per °C. Enable temperature correction when the trace runs warm under load.

Frequently Asked Questions

Why does trace resistance matter?

It creates voltage drop and power loss. Sensitive analog references and high-current power paths are especially sensitive to even small resistances.

Should I use mils or millimeters?

This tool uses millimeters for length, width, and thickness derived from copper weight. Keep units consistent within one calculation.

Does surface finish change DC resistance much?

For typical ENIG or HASL finishes the effect on DC resistance is small compared with copper geometry over useful trace lengths.

When should I enable temperature coefficient?

Use it when the trace operates well above room temperature, such as power distribution traces carrying sustained current.

Is this AC impedance?

No. This calculator returns DC resistance. High-frequency behavior also depends on return path, skin effect, and dielectric loss.

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PCB Trace Resistance Calculator

DC Resistance of a PCB Trace

Resistance Formula

Temperature Coefficient

Frequently Asked Questions

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