Wire Gauge Calculator (AWG Ampacity)

AWG stands for American Wire Gauge, a standardized wire gauge system used in North America for electrical conductors. The system was established in the 19th century and is now maintained as ASTM standard B258. AWG numbers are assigned based on the number of drawing steps used to produce the wire, so the system is not simply linear.

The AWG system is counterintuitive: higher numbers indicate thinner wire. AWG 14 is thinner than AWG 10, and AWG 4/0 (read as four-aught) is the thickest in common residential and light commercial use. The numbering reflects the number of dies the wire is drawn through during manufacture: more draws produce a thinner wire and a higher AWG number. For large conductors above 4/0 AWG, sizing switches to kcmil (thousands of circular mils).

Undersized wire creates excessive resistance, which causes the wire to heat up. This can damage insulation, cause voltage drop at the load, and in severe cases start a fire. The NEC requires wire to be sized so that it does not exceed its rated ampacity under normal operating conditions. Overcurrent protection devices (circuit breakers and fuses) are sized to trip before a conductor is damaged, but they do not substitute for correct wire sizing.

Copper is the standard for most branch circuit wiring because it has lower resistance per cross-section, better corrosion resistance, and a well-established connection system. Aluminum is commonly used for service entrance conductors and large feeders (100A and above) because it is lighter and less expensive per foot. Aluminum wiring requires special connectors rated for aluminum, anti-oxidant compound at connections, and larger conductor sizes compared to copper for the same ampacity. The NEC and local codes govern when each material is appropriate.

When multiple current-carrying conductors are bundled together in a conduit, heat builds up and individual conductors must be derated (their allowable ampacity reduced). NEC Table 310.15(C)(1) specifies derating factors: for 4-6 conductors, derate to 80% of table values; for 7-9 conductors, derate to 70%; and so on. This calculator shows the base NEC 310.15 ampacity for 60 degrees Celsius copper conductors in conduit without additional derating. Always consult a licensed electrician and the full NEC for installation decisions.