Calculate the voltage drop across a wire run from the wire gauge, current, one-way length and system voltage, for both single-phase and three-phase circuits.
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This calculator uses the standard formula: Voltage Drop = (2 × K × I × L) ÷ CM for single-phase circuits, or (√3 × K × I × L) ÷ CM for three-phase circuits, where K is a resistivity constant for the wire material (12.9 for copper, 21.2 for aluminum), I is current in amps, L is the one-way wire length in feet, and CM is the wire's cross-sectional area in circular mils, looked up from standard AWG wire gauge tables.
Excessive voltage drop wastes energy as heat and can cause equipment to run inefficiently or fail to operate correctly. The National Electrical Code recommends keeping voltage drop under 3% for branch circuits and under 5% for the total of feeder and branch circuit combined, though it isn't a hard code requirement in most cases.
In a single-phase circuit, current flows out and back through two conductors, doubling the effective resistance path. Three-phase circuits are more efficient due to their phase relationships, so the standard formula uses √3 (about 1.732) instead of 2.
Use a larger wire gauge (a lower AWG number means a thicker wire with more circular mils), or shorten the run if possible, both reduce voltage drop for the same current.
No, this is a planning estimate only. Always have electrical work verified by a licensed electrician and checked against your local electrical code.
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