Circuit Breaker Size Calculator
Calculate the correct circuit breaker size from load amperage, wire gauge, and the NEC 80% rule.
Avoid tripped breakers and fire risk in any circuit.
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.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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