Voltage drop calculator

Voltage lost along a run for the wire size you choose.

How it works

Voltage drop is conductor resistance times current times the round-trip length. Smaller wire and longer runs lose more. A common target for branch circuits is under 3%.

How to measure

Take the current from the nameplate or watts ÷ volts. Enter one-way length; the tool doubles it.

Tips

High drop makes motors run hot and lights flicker.
Aluminum has roughly 60% more resistance than copper of the same size.
Resistance values are from NEC Chapter 9, Table 8; results are estimates.

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