Voltage Drop Calculator
Calculate the voltage drop across an electrical cable. Enter the supply voltage, current, cable length and wire size to see the drop, voltage at load and percentage loss.
How It Works & Formula
Resistance is R = (resistivity x 2 x length) / wire area. Voltage drop is V = current x R, and percentage drop is (drop / supply) x 100.
Frequently Asked Questions
What is an acceptable voltage drop?
Generally, a voltage drop under 5% is acceptable for most circuits, though 3% is preferred for branch circuits.
Why is the length doubled?
The current travels to the load and back, so the total conductor length is twice the one-way distance.
What units does it use?
Supply voltage in volts, current in amps, cable length in meters, and wire size in square millimeters.