Wire Gauge (AWG) Calculator
Find the correct wire size for any circuit — checks both ampacity and voltage drop per NEC guidelines.
Recommended Wire Gauge
AWG Ampacity & Resistance Reference
| AWG | Copper Ampacity | Alum. Ampacity | Resistance (Ω/1000ft) |
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About Wire Gauge Selection
Choosing the correct wire gauge is critical for electrical safety. An undersized wire overheats, creating a fire hazard. Two key factors determine the minimum required gauge: ampacity (the current-carrying capacity) and voltage drop (the resistance-caused loss over long runs).
NEC 80% Rule: The National Electrical Code requires that continuous loads (running 3+ hours) not exceed 80% of a circuit breaker's rating. This means a 20A breaker should serve at most 16A of continuous load. Always size wire for the breaker, not just the load.
Voltage Drop: NEC recommends keeping voltage drop under 3% for branch circuits and 5% total (feeder + branch). Low-voltage systems like 12V are especially sensitive — a 3% drop on 12V is only 0.36V, so long runs need heavier wire. The formula is: VD = (2 × Length × Current × Resistance) / 1000, where resistance is in ohms per 1000 feet.
Aluminum Wiring: Aluminum has about 84% of copper's current capacity and requires larger conduit fill allowances. It's common for service entrances and large feeders but requires antioxidant compound at connections. Never mix aluminum and copper without rated connectors.