Find the right wire size for any circuit. AWG & metric charts with ampacity, resistance, and diameter. Based on NEC and IEC standards.
Copper ampacity at 60 °C (NM-B / romex). See individual pages for 75 °C and 90 °C ratings.
All wire data calculated from the AWG formula (ASTM B258), material resistivities, and NEC/IEC ampacity standards.
Every AWG size from 4/0 to 40, all 19 IEC metric sizes, 8 conductor materials, and NEC ampacity at 60/75/90°C.
Appliance wiring guides with NEC references, breaker sizes, and wire types. Real-world sizing for dryers, hot tubs, EV chargers, and more.
For a 20-amp circuit, use 12 AWG copper wire (or 10 AWG aluminum). This is the NEC-required minimum for kitchen, bathroom, and garage circuits.
Voltage drop = (2 × length × amps × resistance per foot). NEC recommends keeping voltage drop under 3% for branch circuits. Use our free calculator — enter amps, voltage, distance, and wire gauge to get the exact percentage.
AWG (American Wire Gauge) is the US standard for wire size. Counterintuitively, larger AWG numbers mean thinner wire: 14 AWG is thinner than 10 AWG. Common household sizes: 14 AWG (15A), 12 AWG (20A), 10 AWG (30A), 8 AWG (40A), 6 AWG (55A).