Home energy · electrical safety
How many watts can this breaker carry?
Enter the breaker rating and voltage to see the continuous and absolute wattage limits, and optionally check a specific load.
Short answer
A 15 A breaker on 120 V is 1,800 W at 100% of its rating, and 1,440 W (12 A) for a load that runs 3 hours or more, because UL says a breaker is intended for no more than 80% of its rating for continuous loads unless marked otherwise.
Circuit
Result
Worked example
A 15 A breaker on 120 V: 15 x 120 = 1,800 W at 100%, and 15 x 0.8 = 12 A x 120 V = 1,440 W continuous. A 1,500 W heater draws 1,500 / 120 = 12.5 A. As a continuous load it needs a breaker of at least 15.6 A, so it is over the 15 A circuit's 80% limit. A 20 A breaker on 120 V is 1,920 W continuous; on 240 V it is 3,840 W.
Formula, assumptions and sources
UL's breaker marking and application guide states: unless otherwise marked for continuous use at 100 percent of its current rating, a circuit breaker is intended for use at no more than 80 percent of its rated current where in normal operation the load will continue for three hours or more. Continuous watts = breaker amps x 0.8 x volts. Minimum breaker for a continuous load = load amps / 0.8. This checks the breaker only. Wire size, receptacle rating, other loads on the same circuit, motor starting current and local code all matter and are not checked. The 120 V and 240 V entries are nominal; use your actual service voltage.
Source: UL Solutions, Molded Case Circuit Breaker - Marking and Application Guide (opened 2026-10-08)
Safety and limits
This is a planning aid, not professional advice. Electrical and HVAC work can cause fire, shock and carbon monoxide hazards; have a licensed professional size, install and inspect equipment.
FAQ
How many watts can a 15 amp breaker handle?
At 120 V, 1,800 W at 100% of the rating and 1,440 W for loads that run 3 hours or more.
How many watts can a 20 amp breaker handle?
At 120 V, 2,400 W at 100% and 1,920 W continuous. At 240 V, 4,800 W and 3,840 W.
Can I just swap in a bigger breaker?
No. The breaker protects the wire; a larger breaker on the same wire removes that protection. Any change to a circuit is a job for a licensed electrician.