Voltage drop calculator

Voltage

The circuit voltage at the source: 120 V for most receptacles, 240 V for a dryer or water heater, 208 or 480 V for three-phase.

One-way length

The distance from the panel to the load, measured along the route the wire takes. Don't double it; the calculator accounts for the return path.

Parallel sets

Large feeders sometimes use two or more conductors per phase. Leave at 1 for ordinary circuits.

310.10(G)

Target drop

The NEC suggests no more than 3% on a branch circuit or feeder, and 5% total from service to load. These are recommendations, not requirements, but many specs require them.

210.19 IN 4, 215.2 IN 2