PCB Trace Resistance Calculator

A PCB trace has resistance set by its length, width and copper thickness.

How the Math Works

The PCB Trace Resistance Calculator uses the fundamental formula R = rho * L / (w * t) to determine copper trace resistance. Here, rho (ρ) represents copper's resistivity at 20°C (approximately 1.68 x 10^-8 ohm-meters), L is the trace length, w is the trace width, and t is the trace thickness. This relationship shows resistance increases with longer traces and thinner conductors, while decreasing with wider traces. The formula derives from Ohm's law applied to conductor geometry, where cross-sectional area (width multiplied by thickness) inversely affects resistance.

Practical Applications

To use this calculator, input the trace length, width, and thickness of your PCB copper trace. The calculator automatically applies copper's resistivity value. For example, a 100mm long, 2mm wide, and 0.035mm thick trace would have a resistance of approximately 0.053 ohms. This calculation is essential for designing power delivery networks, signal traces, and thermal relief patterns in PCB layout, helping engineers ensure voltage drops remain within acceptable limits and current carrying capacity meets design requirements.

Day-to-Day Use

Understanding trace resistance helps explain why USB cables feel warm during fast charging or why long Ethernet cables sometimes cause network issues. It's why high-current devices use thick power cables and why circuit boards have wide traces for power rails. This knowledge empowers hobbyists building electronics projects to make better design decisions, troubleshoot unexpected behavior, and appreciate why simply soldering wires together isn't always sufficient for reliable electrical connections in everyday devices.

Worked example

100 mm of 0.5 mm wide, 1 oz trace is about 96 mOhm.

FAQ