Free Breaker Size calculator with clear step-by-step results.
Converts a connected load in watts to circuit current, applies the continuous-load sizing factor that codes require for loads running three hours or more, then rounds up to the next standard breaker rating rather than down. Conductor ampacity must be selected to match or exceed that breaker.
Load current
Amps = watts / (volts x power factor)
Required ampacity
Required = load amps x continuous-load factor (typically 125%)
Not a substitute for design to code. Overcurrent protection, conductor sizing, derating for ambient temperature and conduit fill, and motor or HVAC loads all have specific code rules. Work must be designed and inspected by a licensed electrician.
Thermal-magnetic breakers and conductor insulation are rated for a load that is not continuous. A load drawing full current for three hours or more must be sized at 125% so the assembly does not run at its thermal limit.
No - it protects the conductor. The wire gauge must be chosen for the breaker rating, and appliance protection comes from its own internal fusing or overload device.