This tool, based on the formulas and graphs contained in the standard document [1], calculates the resistance of a copper PCB trace (also known as or track), knowing the trace length, width, thickness and the ambient temperature. The same calculation can be applied to bus bars.

Trace resistance calculation is important, since it allows to evaluate how much power can be dissipated by the trace itself.

Resistance calculation

The PCB internal/external trace resistance shall be calculated according to the following formula:

R = (ρ * L / (T * W)) * (1 + α * (T_AMB – 25 °C))

Where:

R is the trace resistance [Ω] ρ is the resistivity parameter, whose value for copper is 1.7E-6 [Ω · cm] L is the trace length [cm] T is the trace thickness [cm] W is the trace width [cm] α is the resistivity temperature coefficient, whose value for copper is 3.9E-3 [1/°C] T_TEMP is the trace temperature [°C]

Example 1

Inputs L = 5 inch W = 4 mil T = 3 oz/ft² T_AMB = 38 °C

Output R = 0.213 Ω

Example 2

Inputs L = 10.5 inch W = 4.6 mil T = 5.8 oz/ft² T_AMB = 37.5 °C

Output R = 0.200 Ω

Reference

[1] IPC-2221A “Generic Standard on Printed Board Design”

[2] Omicalculator PCB Trace Resistance

[3] Omicalculator Home page