Voltage Drop Calculator
Calculate voltage drop for copper conductors, single or three phase, using NEC-recommended limits. Verify wire runs for HVAC equipment circuits.
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Frequently asked questions
What is voltage drop?
Voltage drop is the reduction in voltage between the source and the load caused by conductor resistance. It increases with higher current, smaller wire, and longer runs.
What voltage drop percentage is recommended?
A common design recommendation is to keep branch circuits at or below 3% voltage drop and total feeder plus branch circuits at or below 5%.
Is the length one-way or round-trip?
This calculator uses one-way length (source to load). The single-phase formula accounts for the return path internally.
Does this calculator support aluminum conductors?
This version is copper-only. Aluminum has different resistance characteristics and requires a different constant or impedance method.
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