PCB Voltage Drop Calculator
Calculate PCB trace resistance, voltage drop, power loss, and rail-voltage loss from current and finished copper geometry.
The calculation adjusts copper resistivity for operating temperature, helping hardware engineers review power distribution, low-voltage rails, and high-current board routing.
Engineering tool
PCB Voltage Drop Calculator
Calculate temperature-adjusted trace resistance, voltage drop, power loss, and rail-voltage loss percentage.
DC or RMS current through the PCB trace.
One-way conductor length used for this resistance calculation.
Finished conductor width, including any neck-down review.
Finished copper thickness; 1 oz is approximately 34.79 µm.
Rail voltage used to calculate percentage drop.
Expected operating copper temperature, not only ambient.
Result console
- Trace resistance
- 53.449451mΩ
- Voltage drop
- 106.898902mV
- Power loss
- 213.797804mW
- Voltage drop percentage
- 2.137978%
- Effective copper resistivity
- 1.859506e-8Ω·m
- Estimated load voltage
- 4.893101V
Voltage drop status
Review
The trace drop is between 1% and 3% of the supply. Review load tolerance and consider a wider trace, thicker copper, shorter route, or copper pour.
Formula reference
PCB Trace Voltage Drop Formulas
Trace resistance is calculated from conductor geometry and copper resistivity adjusted from its 20°C reference value.
ρT = ρ20 × [1 + α × (T - 20)]Cross-sectional area: A = W × tTrace resistance: R = ρT × L / AVoltage drop: Vdrop = I × RPower loss: P = I² × RVoltage drop percentage = Vdrop / Vsupply × 100%Variable definitions
- ρ20
- 1.724 × 10⁻⁸ Ω·m
- α
- copper temperature coefficient, 0.00393 / °C
- T
- operating copper temperature
- L, W, and t
- trace length, width, and thickness
Worked Example
For 2 A through a 100 mm long, 1 mm wide, 1 oz trace at 40°C, the adjusted copper resistivity is approximately 1.859 × 10⁻⁸ Ω·m.
The trace resistance is about 53.44 mΩ, producing approximately 106.9 mV drop and 213.8 mW loss. On a 5 V rail, that is about 2.14% voltage loss.
Engineering Notes
- PCB voltage drop increases with current and trace length.
- Wider traces and thicker finished copper reduce resistance.
- Copper resistance increases as operating temperature rises.
- Low-voltage rails are more sensitive to a given voltage-drop percentage.
- High-current rails should be checked for both voltage drop and thermal rise.
Support reference
FAQ
How do you calculate PCB trace voltage drop?
Calculate trace area from width and copper thickness, use temperature-adjusted copper resistivity to find resistance, then multiply resistance by current: Vdrop = I × R.
Why does PCB trace resistance matter?
Trace resistance causes voltage loss, I²R heating, reduced load voltage, and possible rail-regulation errors. It becomes especially important on long, narrow, or high-current routes.
How does copper thickness reduce voltage drop?
Thicker copper increases trace cross-sectional area. Since resistance is inversely proportional to area, increasing finished copper thickness lowers resistance and voltage drop.
What is an acceptable PCB voltage drop?
The acceptable value depends on load tolerance and rail voltage. One percent is a useful conservative screening target, while sensitive low-voltage rails may require substantially less.
Why does temperature affect copper resistance?
Copper has a positive temperature coefficient of about 0.00393 per °C. As copper temperature rises, resistivity and therefore trace voltage drop increase.
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