PCB Trace Resistance Calculator
DC resistance and voltage drop of a copper trace from length, width and copper weight — with temperature correction.
Rule of thumb: a 1 oz copper trace has a sheet resistance of ~0.5 mΩ per square — a trace 10× longer than wide is ~5 mΩ regardless of absolute size. Sense-resistor layouts and Kelvin connections exist precisely because trace resistance corrupts low-side current measurements.
Trace Resistance Calculator computes the DC resistance and voltage drop of a copper trace — free, instant and private in your browser. Anyone debugging sagging rails, sizing sense lines or budgeting drop on long board routes use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About PCB Trace Resistance Calculator
Trace Resistance Calculator computes the DC resistance and voltage drop of a copper trace using the standard engineering relation: R = ρ·L/(w·t) with copper ρ = 1.72×10⁻⁸ Ω·m, plus ~0.39 %/°C temperature correction. Worked live: a 100 mm × 0.25 mm trace in 1 oz copper is about 196 mΩ — at 1 A that's nearly 0.2 V gone. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use PCB Trace Resistance Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use PCB Trace Resistance Calculator?
- ✓Implements the real formula — R = ρ·L/(w·t) with copper ρ = 1.72×10⁻⁸ Ω·m, plus ~0.39 %/°C temperature correction — with the substitution shown, not a black box
- ✓Built for anyone debugging sagging rails, sizing sense lines or budgeting drop on long board routes
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate trace resistance?+
The DC resistance and voltage drop of a copper trace follows R = ρ·L/(w·t) with copper ρ = 1.72×10⁻⁸ Ω·m, plus ~0.39 %/°C temperature correction. For example, a 100 mm × 0.25 mm trace in 1 oz copper is about 196 mΩ — at 1 A that's nearly 0.2 V gone. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Why does my 3.3 V rail read low at the far end of the board?+
Trace resistance. Long thin power routes drop tens to hundreds of millivolts at modest currents — compute R for the route, multiply by the current, and you will usually find the missing voltage. The fixes are wider copper, a pour, or a higher-layer plane.
Does trace resistance matter for signals too?+
Rarely for logic levels, but it matters in precision analog: a 50 mΩ shared return carrying 100 mA injects 5 mV of error into anything referenced to it — large against a 1 mV sensor signal. That is why Kelvin routing exists.
Is the Trace Resistance Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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