Drop over a run at load, and the smallest conductor that holds your target. Single-phase drop = 2·K·I·L ÷ circular mils; three-phase uses √3 in place of 2. K is 12.9 for copper, 21.2 for aluminum. The Code's informational notes recommend holding branch circuits to about 3% and the whole run to about 5% — recommendations, not mandates.
Volts Phase Material Amps One-way feet Conductor Target %
Reference only. Compiled from the cited official sources as of the date shown; adoptions and rules change. Confirm with the authority having jurisdiction before designing or permitting work.