Circuit Breaker Sizing Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Why breakers are sized above the actual load
Electrical codes require breakers and wiring supplying loads that run continuously for three hours or more to be rated well above the load's actual current draw. Sizing a breaker exactly to the load's current invites nuisance tripping and long-term overheating.
This calculator implements the widely referenced 125% continuous load rule found in electrical codes such as the NEC - always check your local electrical code and consult a licensed electrician for actual installations, since rules vary by jurisdiction and load type.
Worked example
For a continuous load drawing 16A:
Minimum Breaker Rating = 16A x 1.25 = 20 A minimum
In this case 20A lines up exactly with a standard breaker size, but results will not always land neatly on a standard rating - always round up to the next standard breaker size available (typically 15A, 20A, 30A, 40A, 50A) rather than down, even if the calculated minimum falls between two standard sizes.