Voltage Drop Calculator

How it's calculated

R = ρ × L ÷ A
DC / single-phase: ΔV = 2 × I × R
Three-phase (line to line): ΔV = √3 × I × R
% = ΔV ÷ V × 100

Current flowing through a cable loses some voltage to the cable’s own resistance. Copper (1.68 × 10⁻⁸ Ω·m) and aluminium (2.65 × 10⁻⁸ Ω·m) are at 20 °C; conductors at working temperature are a few percent more resistive. Many codes aim for under 3% on a branch circuit and 5% overall. This uses resistance only, a good estimate for small and medium cables; large AC feeders also need reactance and power factor.