PCB trace width and current calculator

IPC-2152. The standard publishes charts, not equations. The calculator uses the curve fit of those charts by Brooks and Adam: ΔT = K · Ia · Wb · Thc, with width W and thickness Th in mils. External layers use K = 215.3, a = 2.0, b = −1.15, c = −1.0. Internal layers use a separate set for each copper weight (½ to 3 oz). Solving for W or I gives the minimum width or the maximum current.

IPC-2221. The older chart is the familiar I = k · ΔT0.44 · A0.725, with A the cross-section in mil², k = 0.048 for external and k = 0.024 for internal conductors.

Resistance. R = ρ(T) · L / (W · t), with ρ(20 °C) = 1.724×10⁻⁸ Ω·m and a temperature coefficient of 0.00393 /K, evaluated at ambient + temperature rise.

Which one to use. IPC-2152 replaced IPC-2221 for current capacity. Its baseline is conservative: a single trace on a board with no nearby copper planes, in still air. A plane under the trace, a thicker board or forced air reduce the real temperature rise considerably. At high currents IPC-2152 asks for wider external traces than IPC-2221.

References

1. IPC-2152, Standard for Determining Current Carrying Capacity in Printed Board Design, 2009.
2. D. Brooks, J. Adam, “Trace Currents and Temperatures Revisited”, 2015 (curve fit, Table 3-1).
3. IPC-2221, Generic Standard on Printed Board Design, section 6.2 (conductor current capacity).