Electrical Wire Gauge Calculator (AWG)

Choosing the Right Wire Size

Wire gauge must match the circuit amperage — undersized wire overheats and causes fires. NEC (National Electrical Code) minimums for copper: 15A → 14 AWG, 20A → 12 AWG, 30A → 10 AWG, 40A → 8 AWG, 50A → 6 AWG. For long runs (over 50 feet), voltage drop becomes a concern — upsize one gauge to keep voltage drop under 3%. Aluminum wire requires 2 sizes larger than copper for the same amperage.

Voltage Drop and Long Runs

NEC recommends keeping voltage drop below 3% for branch circuits and 5% total (feeder + branch). On a 120V circuit, 3% is only 3.6 volts. Long wire runs increase resistance, causing lights to dim and motors to overheat. At 100 feet on a 20A/120V circuit, 12 AWG copper has about 3.2% voltage drop — borderline. Use 10 AWG for runs over 75 feet on 20A circuits.