Circuit Breaker Size Calculator
Calculate the correct circuit breaker size for any electrical circuit based on load amperage, wire gauge, and NEC 80% rule.
Avoid tripped breakers and fire risk.
Circuit breakers protect wiring from overheating by cutting power when current exceeds a safe level. Choosing the wrong size — too small or too large — causes problems ranging from nuisance trips to house fires.
The NEC 80% Rule:
The National Electrical Code (NEC) requires that continuous loads (running for 3+ hours) use no more than 80% of the breaker’s rated capacity.
Minimum Breaker Size = Total Load (amps) ÷ 0.80
If your circuit draws 16 amps continuously:
16 ÷ 0.80 = 20A breaker minimum
Standard breaker sizes (US): 15A → 20A → 25A → 30A → 40A → 50A → 60A → 70A → 80A → 100A → 125A → 150A → 200A
Always round up to the next standard size after the calculation.
Wire gauge must match the breaker:
| Breaker Size | Minimum Wire Gauge | Wire Ampacity |
|---|---|---|
| 15A | 14 AWG | 15A |
| 20A | 12 AWG | 20A |
| 30A | 10 AWG | 30A |
| 40A | 8 AWG | 40A |
| 50A | 6 AWG | 55A |
| 60A | 6 AWG | 55A |
| 70–80A | 4 AWG | 70A |
| 100A | 2 AWG | 95A |
Never install a breaker larger than the wire can handle — this is the most dangerous electrical mistake homeowners make.
Common circuits and typical breaker sizes:
| Circuit | Typical Breaker |
|---|---|
| General lighting / outlets | 15A |
| Kitchen small appliances | 20A |
| Dishwasher | 20A |
| Refrigerator | 15–20A |
| Microwave (dedicated) | 20A |
| Washing machine | 20A |
| Garbage disposal | 20A |
| Electric dryer | 30A |
| Electric range / oven | 40–50A |
| Central AC (3–5 ton) | 30–60A |
| Electric water heater | 30A |
| Hot tub / spa | 50–60A |
| EV charger (Level 2, 7.2kW) | 40–50A |
Important: Always have a licensed electrician verify calculations and perform wiring work in your jurisdiction. Electrical codes vary by location.