Breaker Size Calculator
Determine the correct circuit breaker size.
How It Works
Load current = Watts ÷ Voltage. Continuous loads derate × 1.25. Breaker = next standard size ≥ derated amps.
Example
2,400 W at 120 V continuous: 20 A × 1.25 = 25 A → 25 A breaker.
Frequently Asked Questions
What is a continuous load?
A load expected to run 3+ hours, like lighting and some appliances — NEC requires a 125% safety margin.
What are standard breaker sizes?
15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100 A.
Can I use the next size up?
No — the breaker must be rated for the wire, not just the load. Always confirm with a licensed electrician.