PCB Trace Resistance Calculator
Estimate copper trace resistance, voltage drop, and power dissipation using board geometry and temperature.
Why PCB trace resistance matters
Trace resistance is easy to ignore when routing a board, but it can impact performance in very practical ways. Even a few milliohms can create measurable voltage drop in power rails, generate heat, and influence analog accuracy. In high-current designs, long or narrow traces can become a bottleneck long before components reach their rated limits.
This calculator helps you quickly estimate DC resistance for a copper trace so you can make better routing decisions early in the design cycle.
Formula used in this calculator
The calculator uses the standard conductor resistance equation:
R = ρ × L / A
- R = resistance in ohms (Ω)
- ρ = copper resistivity in ohm-meters (Ω·m)
- L = trace length in meters (m)
- A = cross-sectional area in square meters (m²)
Copper resistivity increases with temperature. The calculator compensates using:
ρ(T) = ρ20 × [1 + α × (T − 20°C)]
Where ρ20 = 1.724×10-8 Ω·m and α = 0.00393 /°C.
Input guide
1) Length
Total electrical path length of the trace. Include all segments and bends.
2) Width
Finished trace width after etching. Real width can be smaller than nominal depending on process tolerance.
3) Copper thickness / weight
You can choose a common copper weight or enter a custom thickness directly.
| Copper Weight | Approx. Thickness |
|---|---|
| 0.5 oz/ft² | 17.4 µm |
| 1 oz/ft² | 34.8 µm |
| 2 oz/ft² | 69.6 µm |
| 3 oz/ft² | 104.4 µm |
4) Temperature
Higher temperature increases resistance. Use realistic operating temperature, not just room temperature, for power calculations.
5) Current (optional)
When current is entered, the calculator also reports:
- Voltage drop: V = I × R
- Power dissipation: P = I² × R
Practical design tips
- Wider traces reduce resistance linearly.
- Thicker copper helps for high-current rails and thermal margin.
- Shorter routes reduce both loss and voltage drop.
- Parallel traces or copper pours can significantly cut effective resistance.
- Via resistance can be important in multilayer current paths—don’t ignore it.
Common use cases
- Checking IR drop on 3.3V and 5V distribution nets
- Sizing battery and motor-current paths
- Estimating heating in low-ohmic sense routing
- Comparing 1 oz versus 2 oz copper during stack-up selection
Limitations to keep in mind
This is a DC resistance estimate for a uniform copper trace. It does not model skin effect at high frequency, current crowding near pads/vias, plating variation, or thermal gradients across the board. For precision work, combine this quick estimate with PCB field solvers and manufacturer process data.