Electrical Wire Size Calculator
Selecting the correct wire gauge is a safety and code compliance requirement. Wire that is too small for the amperage it carries overheats, creating a fire hazard and violating the National Electrical Code (NEC). This calculator determines the minimum wire size based on amperage, circuit length, and acceptable voltage drop.
Wire Gauge Calculator (AWG)
Wire sizing must comply with NEC Article 310 and local amendments. Temperature ratings, conduit fill, ambient temperature, and bundling derating factors may require upsizing. Always verify with a licensed electrician.
NEC Wire Ampacity Table (Copper, 75°C, NEC 310.16)
| AWG / kcmil | Copper (75°C) | Aluminum (75°C) | Typical Use |
|---|---|---|---|
| 14 AWG | 20A | — | Lighting circuits (15A breaker) |
| 12 AWG | 25A | 20A | General receptacles (20A breaker) |
| 10 AWG | 35A | 30A | Dryer, water heater (30A) |
| 8 AWG | 50A | 40A | Range, large appliances (40–50A) |
| 6 AWG | 65A | 50A | Sub-panels, large HVAC (50–60A) |
| 4 AWG | 85A | 65A | Feeder circuits, EV charger |
| 3 AWG | 100A | 75A | 100A sub-panel feeder |
| 2 AWG | 115A | 90A | Large sub-panels |
| 1 AWG | 130A | 100A | Service entrance |
| 1/0 | 150A | 120A | 150A service |
| 2/0 | 175A | 135A | 200A service |
| 3/0 | 200A | 155A | 200A service (aluminum) |
| 4/0 | 230A | 180A | 200A+ service |
Frequently Asked Questions
What is voltage drop and why does it matter?
Voltage drop is the reduction in voltage that occurs as electricity travels through wire. Longer runs and smaller wire gauges increase voltage drop. The NEC recommends no more than 3% voltage drop for branch circuits and 5% total for the combination of branch circuit and feeder. Excessive voltage drop causes lights to dim, motors to overheat, and equipment to malfunction.
When should I use aluminum wire instead of copper?
Aluminum is commonly used for larger feeder and service entrance conductors (4 AWG and above) because it costs significantly less than copper. For branch circuits (general wiring inside walls), copper is standard. Aluminum requires larger wire sizes for the same ampacity and requires compatible connectors rated for aluminum to prevent oxidation at connections.
Do I need to upsize wire for conduit runs?
Yes, in some cases. When multiple current-carrying conductors share a conduit, NEC Table 310.15(C)(1) requires derating the ampacity. For example, 4–6 conductors in a conduit reduces ampacity to 80% of the table value, requiring the next larger wire size.