Voltage Drop Calculator (NEC)

Calculate voltage drop for copper or aluminum conductors per NEC. Select wire size (AWG), enter current and distance — the calculator warns you if drop exceeds the NEC 3% recommendation.

Voltage Drop Calculator

NEC-based voltage drop for copper or aluminum conductors (AWG).

System

Wire material

Wire size (AWG)

Current (amps)

One-way length (feet)

Supply voltage (V)

Voltage drop–

Drop percentage–

Voltage at load–

⚠ Drop exceeds 3% — NEC recommends max 3% on branch circuits. Use a larger wire.

1φ: VD = 2 × K × I × L ÷ CM · 3φ: VD = 1.732 × K × I × L ÷ CM (K = 12.9 Cu / 21.2 Al)