Voltage-drop calculator
Uses the standard textbook formula: VD = (k × K × I × L) ÷ CM. Here k = 2 for single-phase or 1.732 for three-phase, K is the conductor's approximate resistance constant, I is load amps, L is the one-way length in feet, and CM is the wire's area in circular mils.
Read this first. This is an estimate for planning and study. The K values are common textbook approximations for uncoated conductors at typical operating temperatures. The calculator ignores reactance, temperature correction and power factor. Wire-size areas are computed from the AWG geometric formula, not copied from any code table. A widely used design target is about 3% drop on a branch circuit and 5% total, but your local rules, the engineer, and the inspector have the final say.