Voltage Drop Calculator — Free Online Calculator
Calculate voltage drop across any wire run. Enter wire gauge, distance, load, and voltage to find exact voltage loss and percentage.
How to Use This Calculator
Select the wire gauge, enter the load current in amps, the one-way wire run distance in feet, and the source voltage. Choose copper or aluminum and single or three-phase. The calculator computes the exact voltage drop across the wire run and tells you whether it meets NEC recommendations.
The Formula Explained
Voltage drop is calculated using the circular mil method: VD = (K × I × D × 2) / CM, where K is the resistivity constant (10.37 for copper at 75°C, 17.02 for aluminum), I is the current in amps, D is the one-way distance in feet, and CM is the circular mil area of the conductor. For three-phase circuits, the factor 2 is replaced by √3 (1.732). The result tells you how many volts are lost in the wire, what percentage of the source voltage that represents, and the actual voltage delivered to the load.