PCB Trace Resistance Calculator

About the PCB Trace Resistance Calculator

The PCB Trace Resistance Calculator computes the DC resistance of copper traces on printed circuit boards, accounting for trace geometry, copper weight, and operating temperature. Accurate resistance estimation is critical for power distribution network design, voltage drop budgeting, and thermal analysis. It gives you a quick way to check whether a trace is still acceptable after layout changes or temperature rise.

Copper resistivity increases with temperature—about 0.39% per degree Celsius. A trace that measures 10mΩ at room temperature will be 14mΩ at 125°C, a 40% increase that significantly affects voltage drop calculations for high-current designs. This calculator includes full temperature compensation using copper's thermal coefficient of resistance.

The tool supports both metric and imperial units, handles all standard copper weights from 0.5oz to 6oz, and provides multi-segment analysis for traces with different widths along their length. It also calculates skin effect depth for AC applications and shows how resistance varies with frequency, complementing the DC analysis with high-frequency considerations.

When This Page Helps

Use this calculator when you need to check whether a PCB trace can carry current without an excessive voltage drop or heating problem. It is useful for power-path design, copper-width tradeoffs, and spotting cases where temperature turns a marginal trace into a bad one. It also helps you compare alternate routing options before committing to a board spin.

How to Use the Inputs

1. Enter trace width and length in your preferred units (mil, mm, or inches)
2. Select the copper weight/thickness for your PCB stackup
3. Set the operating temperature for temperature-compensated resistance
4. Enter the expected current to see voltage drop and power dissipation
5. Add multiple trace segments with different widths for complex routing
6. Check AC resistance at your signal frequency if skin effect matters

Example Calculation

Tips & Best Practices

• Always use operating temperature (not 25°C) for resistance calculations — the difference can be 30%+ at elevated temperatures
• Add via resistance for each via transition in your power path (0.5-1mΩ per standard via)
• For voltage drops over 2% of your supply rail, you need wider traces or heavier copper
• Use copper pours tied to power nets to massively reduce distribution resistance
• Verify calculations with a 4-wire Kelvin measurement on prototype boards

Temperature Compensation in Practice

PCB designers often calculate trace resistance at room temperature and overlook the significant increase during operation. A device operating at 85°C ambient with additional self-heating can push trace temperatures to 100-120°C, increasing resistance by 25-40% compared to room temperature. For power supply accuracy, always use worst-case temperature for voltage drop budgeting.

Multi-Segment Trace Analysis

Real PCB traces often change width along their route—wider in open areas, narrower through BGA escape channels. Total resistance is the sum of each segment: R_total = Σ(ρ × Lᵢ / Aᵢ). This calculator supports multiple segments, accounting for width changes, layer transitions (with via resistance), and different copper weights on different layers.

DC vs. AC Resistance

At DC and low frequencies, current distributes uniformly through the trace cross-section. At higher frequencies, skin effect concentrates current near the surface, effectively reducing the conductive area and increasing resistance. The skin depth formula δ = √(ρ/(πfμ₀)) gives the depth at which current density falls to 1/e (37%) of the surface value. At 1 GHz, copper skin depth is only 2.1µm—much thinner than any standard copper weight.

Frequently Asked Questions

• How does temperature affect trace resistance?

  Copper has a temperature coefficient of +0.00393/°C. At 100°C, resistance is 31.4% higher than at 20°C. Always use operating temperature, not room temperature, for voltage drop calculations in power designs.

• What is the resistivity of copper?

  Pure copper (annealed) has a resistivity of 1.724 × 10⁻⁶ Ω·cm at 20°C. PCB copper may be slightly higher due to electroplating impurities—some designers use 1.8 × 10⁻⁶ for a safety margin.

• When does skin effect matter for PCB traces?

  Skin depth in copper at 1 MHz is about 66µm, and at 100 MHz about 6.6µm. For 1oz copper (35µm), skin effect begins to increase resistance above ~5 MHz. For DC and low-frequency power, skin effect is negligible.

• How do I reduce trace resistance?

  Use wider traces, heavier copper (2oz+), parallel traces on multiple layers connected by vias, shorter routing, or copper pours. Each doubling of width or copper weight halves resistance.

• Via resistance—is it significant?

  A standard via (10mil drill, 1oz plating, 62mil board) has about 0.5-1mΩ resistance. For low-current signals this is negligible, but for 10A+ power paths, you need many parallel vias to match trace resistance.

• What voltage drop is acceptable?

  Typically 1-3% of the supply voltage. For a 3.3V rail, keep total drop under 33-100mV. For 1.0V core voltage, the budget might be only 10mV total across the entire distribution network.