PCB Trace Resistance Calculator — DC Resistance & Voltage Drop
Find the DC resistance of any PCB copper trace and the resulting voltage drop and power dissipation at a given current. Enter the trace geometry and operating temperature — copper resistivity increases with temperature, so this matters on hot boards.
mm
mm
Copper weight
°C
A
DC resistance at the specified operating temperature
- 1
Baseline resistance R₂₀ (mΩ)
ρ × 100 ÷ (0.5 × 0.035) × 1000 = 98.514 - 2
Temperature correction factor
1 + 0.00393 × (25 − 20) = 1.01965Copper resistivity increases ~0.393% per °C above 20 °C. - 3
Trace resistance (mΩ)
98.514 × 1.01965 = 100.450
How does this calculator work?
PCB trace DC resistance: R = ρ × L / (W × T), with ρ_Cu = 1.724 × 10⁻⁵ Ω·mm. A 100 mm, 1 mm wide, 1 oz trace has about 49 mΩ at 20 °C. Operating temperature shifts resistance by 0.393%/°C. Multiply by current to get voltage drop (V = IR) and by current squared for power loss (P = I²R).
Formula
How this is calculated
A copper PCB trace is simply a conductor with a rectangular cross-section. Its DC resistance is R = ρ × L / (W × T), where ρ is the resistivity of copper (1.724 × 10⁻⁸ Ω·m = 1.724 × 10⁻⁵ Ω·mm at 20 °C), L is the trace length, W is the width and T is the copper thickness. All dimensions are in millimetres, giving resistance in ohms. For a 100 mm long, 0.5 mm wide, 1 oz (0.035 mm) trace, R ≈ 1.724e-5 × 100 / (0.5 × 0.035) ≈ 0.0985 Ω ≈ 98.5 mΩ.
Copper resistance increases linearly with temperature at a rate of about 0.393% per degree Celsius (temperature coefficient α = 0.00393 /°C). On a PCB running at 85 °C ambient with trace self-heating, the effective resistance can be 15–25% higher than the 20 °C value. The calculator applies this correction using the operating temperature you specify.
The sheet resistance (mΩ per square) shown in the stats grid is a property of the copper foil weight alone — it equals ρ/T. A "square" of trace has the same resistance regardless of side length, so sheet resistance is useful when estimating multiple traces of the same weight. Multiply sheet resistance by the number of squares (L/W) to get trace resistance — which is exactly what the formula computes.
Frequently asked questions
On a 3.3 V power rail carrying 2 A, a trace with 50 mΩ resistance drops 100 mV (2 A × 0.05 Ω = 0.1 V). That is a 3% supply droop — significant for precision ADCs or low-dropout regulators. Long power traces must be wide enough to keep resistance and voltage drop within the load's input tolerance.
No — this is a DC resistance model only. At high frequency, current concentrates near the conductor surface (skin effect), increasing effective resistance. At 1 GHz the skin depth in copper is about 2.1 µm, so only a thin shell of the trace carries current. Use an RF trace resistance model or EM simulator for AC or high-frequency calculations.
Options include: adding a second identical trace in parallel (halves resistance), adding copper fills or pours connected to the trace, specifying heavier copper (2 oz instead of 1 oz) in your next fabrication run, or rerouting with a shorter/wider path. For power rails, a copper pour with thermal relief on component pads is the most common approach.
Also known as
TG we-Calculate Editorial Team. (2026). PCB Trace Resistance Calculator — DC Resistance & Voltage Drop [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/pcb-trace-resistance-calculator
TG we-Calculate Editorial Team. "PCB Trace Resistance Calculator — DC Resistance & Voltage Drop." TG we-Calculate. 2026. https://we-calculate.com/calculator/pcb-trace-resistance-calculator.
TG we-Calculate Editorial Team, "PCB Trace Resistance Calculator — DC Resistance & Voltage Drop," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/pcb-trace-resistance-calculator
@misc{wecalculate_pcb_trace_resistance_calculator, title = {PCB Trace Resistance Calculator — DC Resistance & Voltage Drop}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/pcb-trace-resistance-calculator}}, year = {2026}, note = {TG we-Calculate} }
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