How to Use the Outlet Circuit Load Calculator
If a breaker trips often or an outlet feels warm to the touch, the circuit is likely being asked to carry more than it safely can. This calculator takes your breaker rating (15A or 20A at 120V) and the type of load — continuous or non-continuous — and compares your connected load against the circuit's allowed capacity.
Under NEC 210.19(A)(1) and 210.20(A), a load that runs continuously for three hours or more must not exceed 80% of the breaker's rating; the informal name for this is the "80% rule." A 20A circuit, for example, can carry the full 2,400W (120V x 20A) for short, non-continuous loads, but a continuous load like space heaters should stay under about 1,920W.
If your usage comes out above the allowed capacity, reduce connected devices or split them across separate circuits. Frequent tripping is a sign to have a licensed electrician inspect the wiring and circuit layout.
Frequently Asked Questions
Technically the breaker can carry its full rated current, but for loads that run continuously (3 hours or more), NEC 210.19(A)(1) and 210.20(A) require sizing so the load doesn't exceed 80% of the breaker rating — leaving headroom prevents nuisance tripping and overheating.
Yes, but the combined simultaneous load of everything plugged into that circuit must stay within the capacity this calculator shows. Large, dedicated appliances are usually better placed on their own circuit.