PCB trace resistance calculator
DC resistance of a copper trace at temperature, with the voltage drop and power at a given current.
- Voltage drop at 1 A
- 200.9 mV
- Power dissipated
- 200.9 mW
- Sheet resistance
- 502 µΩ Per square of this copper weight.
- Squares (length / width)
- 400
- Cross-section
- 0.00875 mm²
- IPC-2221 rise, outer layer
- 13.5 °C Internal layers run hotter: use the trace width calculator.
How this is calculated
R = ρ20 · (1 + 0.00393 · (T − 20)) · L / (w · t) t = 1.378 mil (35 µm) per oz/ft² Rs = ρ / t sheet resistance, Ω per square V = I · R, P = I² · R ΔT = ( I / (0.048 · A^0.725) )^(1 / 0.44) IPC-2221 external, A in mil²
- Copper
- Resistivity 1.724 × 10⁻⁸ Ω·m at 20 °C (annealed copper, IACS), coefficient 0.00393 per °C. 1 oz/ft² is taken as 1.378 mil (35 µm).
- Assumes
- Rectangular cross-section at nominal thickness, DC. Real outer layers are plated up and etched to a trapezoid, so measured resistance can differ by the thickness and width tolerance.
- Temperature
- Enter the copper temperature, not ambient. The IPC-2221 rise is shown so you can add it to ambient and run again.
- IPC-2221B, Generic Standard on Printed Board DesignRevision B, 2012, section 6.2
- Eric Bogatin, Looking Under the Sheets at ResistancePrinted Circuit Design and Fab, October 2007
Questions
0.49 mΩ per square at 20 °C for 35 µm of annealed copper. A trace of length L and width w has L/w squares, so a 1 in by 10 mil trace is 100 squares and about 49 mΩ. Half-ounce copper is twice that.
Copper rises 0.393 % per °C. A trace measured at 25 °C has 23.1 % more resistance at 85 °C, which matters for current sense paths and long power runs.
Outer layers are plated, so finished copper is often thicker than the base foil, and etching leaves a trapezoid narrower at the top. Both shift resistance by the fab tolerance. For a sense resistor path, use a Kelvin connection instead of relying on the trace.
No, it is DC. At high frequency current crowds toward the surface (skin effect) and resistance rises once the skin depth is smaller than the copper thickness. Switching regulator loops and RF lines need an AC model.