How to Use the Circuit Breaker Amperage Calculator
A breaker that's too small trips constantly under normal use, while one that's too large may not trip fast enough during a real overload. This calculator converts your total connected wattage into amperage at your chosen voltage, adds a 25% safety margin for continuous loads, and rounds up to the nearest standard NEC breaker size.
For a standard 120V outlet circuit, common breaker sizes are 15A and 20A. Large 240V appliances like electric dryers, ranges, or EV chargers typically use 30A, 40A, or 50A breakers. For example, an 1,800W load on a 120V circuit draws 15A, which with the 25% margin rounds up to a 20A breaker.
This tool gives a general planning estimate only — actual circuit sizing depends on wire gauge, run length, and local electrical code. Always have new circuits installed or verified by a licensed electrician.
Frequently Asked Questions
Continuous loads should not run at 100% of a breaker's rating. Adding roughly a 25% margin and rounding up to the nearest standard NEC breaker size keeps the circuit from tripping under normal use.
It means your connected load is exceeding the breaker's capacity. Recalculate your total wattage and consult a licensed electrician before upgrading to a larger breaker.