🔧 Breaker Size Calculator
Enter your load’s current draw and whether it’s a continuous load to find a recommended standard circuit breaker size, based on the common NEC 125% rule.
How breaker size is chosen
A circuit breaker protects wiring from overheating by tripping before current exceeds a safe level. Choosing the right size means accounting for both the load’s current draw and how long it runs continuously.
The formula
Many electrical codes (including the NEC in the US) require continuous loads, those running 3 hours or more, to be sized at only 80% of a breaker’s rating, which is equivalent to sizing the breaker at 125% of the load current: Minimum Rating = Load Current × 1.25. Non-continuous loads generally just need a breaker rated at or above the load current. The calculator then rounds up to the next standard breaker size.
This is a simplified educational estimate of common practice, not a substitute for a licensed electrician or the full requirements of your local electrical code, which also considers wire ampacity, ambient temperature, and other derating factors. Always have electrical work reviewed by a qualified professional.