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About the Voltage Drop Calculator
This calculator computes the voltage drop across an electrical circuit based on wire size, material, load current, source voltage, and run length. You get the drop in volts, the percentage of the source voltage, and the resulting voltage at the load.
It applies the standard voltage drop formula VD = 2 × K × I × D / CM for single-phase circuits, where K is the conductor resistivity, I the load current, D the one-way length, and CM the circular mil area of the wire. Three-phase circuits use a factor of 1.732 instead of 2. Enter the one-way distance, not the round-trip length. Most electricians keep branch circuit drop at or below 3 percent, so step up the wire size if the result exceeds that limit.
- Select the wire material and gauge, such as 12 AWG copper.
- Enter the load current, system voltage, phase, and one-way circuit length.
- Read the voltage drop and percentage, then adjust the wire size if needed.