PCB Trace Voltage Drop Calculator
Resistance, voltage drop, % of supply and power loss along a copper trace.
What it does
Calculates the resistance of a copper trace and how much voltage and power it loses at a given current, corrected for copper temperature.
Where it's used
Checking power rails to processors and sensors, LED strips, and long ground returns.
How to use it
- Enter the trace width and copper weight.
- Enter the length and current.
- Enter the copper temperature.
- Enter the supply voltage to see the drop as a percentage.
The formula explained
- R
- ρ(T) × L / (W × t)
- ρ(T)
- copper resistivity corrected for temperature
- V
- I × R — voltage lost
- P
- I²R — heat in the trace
Worked example
A 0.5 mm, 150 mm trace carrying 1.5 A from a 5 V supply.
Inputs:
- Trace width: 0.5 mm
- Copper weight: 1 oz (35 µm)
- Trace length: 150 mm
- Current: 1.5 A
- Copper temperature: 45 °C
- Supply voltage: 5 V
The calculator gives:
- Voltage drop: 244.9 mV
- Trace resistance: 163.3 mΩ
- Power loss: 367.4 mW
Tips and common mistakes
- Keep drop under about 1–2 % on sensitive rails.
- The return (ground) path drops voltage too — consider the whole loop.
- Wider traces, copper pours or heavier copper reduce the drop.
Questions people ask
Is there a quick way to estimate trace resistance?
Count “squares”: length divided by width. 1 oz copper has about 0.5 mΩ per square at room temperature, slightly more when warm. The example 150 mm × 0.5 mm trace is 300 squares, about 160 mΩ.
How wide must the trace be for under 1 % drop?
In the example, 1 % of 5 V is 50 mV at 1.5 A, so the trace may have about 33 mΩ. A 2.5 mm trace of the same length gives 49 mV — 0.98 %.
Can the regulator make up for the drop?
Many regulators have a remote “sense” pin. Connecting it at the load instead of at the regulator’s output makes the regulator correct for the drop along the trace.
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