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How Many Watts Can a 15, 20 or 30 Amp Circuit Handle?

Q: How many watts can a 20 amp breaker handle?

2,400 watts at 120 volts (20 A × 120 V) as a short-term maximum. For continuous loads running three hours or more, the NEC 80% rule lowers that to 1,920 W. A circuit continuously drawing more than 1,920 W is overloaded by code even if the breaker has not tripped yet — breakers tolerate brief overloads, which is why a 2,000 W heater can run for a while before the breaker lets go.

Q: How many outlets can I run on a 20 amp circuit?

By US code there is no outlet-count limit on a general 20 A circuit — the rule is that the planned load must stay under capacity, with continuous loads under 80% (1,920 W). In practice, kitchens, bathrooms and laundry rooms have their own circuit requirements, and good practice on a general circuit is around 10–13 outlets. What matters is what you plug in: thirteen phone chargers are nothing; three space heaters trip the breaker.

Q: What happens if I exceed 80% of a breaker's rating?

For short bursts, usually nothing — breakers are designed to carry moderate overloads for a while before the thermal element trips. Sustained operation above 80% heats the wiring in the walls, which degrades insulation over time and is the fire risk the rule exists to prevent. A breaker that trips repeatedly under normal use is telling you the circuit is undersized for the load, not that the breaker is faulty.

Q: Does a 240 V circuit handle twice the watts of a 120 V circuit at the same amps?

Yes. Watts equal amps times volts, so a 20 A, 240 V circuit handles 4,800 W versus 2,400 W for a 20 A, 120 V circuit — and 3,840 W versus 1,920 W at the 80% continuous limit. This is why large loads like dryers and water heaters use 240 V: double the power delivery at the same breaker size and wire gauge.

Updated October 29, 2026 · 7 min read

direct answer

A circuit handles amps × volts watts: a 15 A, 120 V circuit maxes at 1,800 W (1,440 W continuous), a 20 A circuit at 2,400 W (1,920 W continuous) and a 30 A, 240 V circuit at 7,200 W (5,760 W continuous). The continuous figure is the one that matters for anything running 3+ hours — heaters, grow lights, servers — because the US National Electrical Code requires continuous loads to stay under 80% of the breaker rating. Check any breaker in two seconds with the Amps to Watts Calculator.

The breaker number is not the usable number. Here is the full wattage table for every common residential breaker, the 80% rule that decides what you can actually plug in, and how to check a real circuit before it trips.

The circuit capacity table

Maximum watts (breaker × volts) and the NEC 80% continuous-load limit for each common residential circuit. Continuous loads — anything expected to run three hours or more — must stay in the right-hand column:

Breaker	Voltage	Typical use	Max watts	80% continuous limit
15 A	120 V	Bedrooms, living rooms, lighting	1,800 W	1,440 W
20 A	120 V	Kitchens, bathrooms, laundry, garages	2,400 W	1,920 W
30 A	240 V	Electric dryer, water heater, small AC	7,200 W	5,760 W
40 A	240 V	Large AC, range sub-panel	9,600 W	7,680 W
50 A	240 V	Electric range, EV charger (40 A), RV hookup	12,000 W	9,600 W
60 A	240 V	Large AC, hot tub, sub-panel	14,400 W	11,520 W
100 A	240 V	Whole-home service entrance	24,000 W	19,200 W

Reading the table: a 20 A kitchen circuit can run a 1,200 W microwave (1,200 W < 1,920 W continuous) plus a 600 W coffee maker with margin — but not a 2,000 W countertop oven for a three-hour slow roast, which exceeds even the non-continuous limit. And a 15 A bedroom circuit can handle a 1,500 W space heater only in short bursts: at 1,500 W continuous it is over the 1,440 W limit, which is exactly why space heaters trip bedroom breakers.

The 80% rule, in one paragraph

US electrical code (NEC 210.19 and 210.20) requires that branch circuits serving continuous loads — defined as loads expected to run at maximum current for three hours or more — be sized so the load does not exceed 80% of the breaker rating. The reasoning is heat: a breaker at full rated current warms the wire feeding it, and sustained warmth ages insulation. The rule turns "how many watts can a 20 amp breaker handle" into two answers: 2,400 W momentarily, 1,920 W for real use. Space heaters, dehumidifiers, aquarium gear, server racks, grow lights and EV charging are all continuous loads in practice, even if nobody calls them that.

How to check a circuit before you plug in

Find the breaker. Open the panel and read the number on the handle — 15, 20, 30. The voltage follows the outlet style: standard two/three-prong outlets are 120 V; the big plugs (dryer, range, EV) are 240 V.
Multiply. Breaker amps × volts = maximum watts; × 0.8 for the continuous limit. Or select the preset in the calculator — it lists every breaker above and shows both numbers.
Add up the loads. Appliance wattages are on nameplates or in manuals. Anything resistive (heaters, kettles, toasters) draws its rated watts constantly; motors and compressors add a starting surge of two to three times the running watts.
Respect the weakest link. The breaker protects the wire in the wall, but a long, thin extension cord has its own — lower — limit. A 16-gauge cord is rated around 1,250 W regardless of what the wall circuit can deliver.

The five mistakes that trip breakers

Using the max number as the budget. Budgeting 2,400 W on a 20 A circuit ignores the 80% rule; budget 1,920 W and the breaker stays quiet.
Forgetting that loads add up. The circuit capacity is shared by everything on it. The fridge compressor starting while the kettle boils and the toaster runs is what trips "out of nowhere".
Confusing VA and W on motors. A compressor rated "15 A" on its nameplate may draw its current at power factor 0.8, so it delivers fewer watts — but the breaker sees the full 15 A either way. Breakers care about amps, not watts.
Daisy-chaining power strips. Each strip adds contact resistance and another fuse point; the strip's own rating (often 1,800 W) can be lower than the wall circuit's.
Upsizing the breaker to stop nuisance trips. Never replace a 15 A breaker with a 20 A without rewiring — the wire gauge is matched to the breaker, and a larger breaker on thin wire removes the fire protection entirely.

check any breaker

Amps to Watts Calculator

Pick a preset (15 A outlet, 20 A kitchen, 30 A dryer, 50 A range, 100 A service) and get the maximum watts, the NEC 80% continuous limit and the current draw — all in one view.

Check a circuit

Keep reading

Working in reverse — you have a wattage and need the breaker? The amps to watts chart covers 1–200 A at 12 V, 120 V and 240 V. Want the concepts behind the numbers? Amps vs watts vs volts explains what each unit measures and why breakers are rated in amps while bills count watts.

faq

Frequently Asked Questions

The follow-ups people ask right before plugging something in.

How many watts can a 20 amp breaker handle?

2,400 watts at 120 volts (20 A × 120 V) as a short-term maximum. For continuous loads running three hours or more, the NEC 80% rule lowers that to 1,920 W. A circuit continuously drawing more than 1,920 W is overloaded by code even if the breaker has not tripped yet — breakers tolerate brief overloads, which is why a 2,000 W heater can run for a while before the breaker lets go.

How many outlets can I run on a 20 amp circuit?

By US code there is no outlet-count limit on a general 20 A circuit — the rule is that the planned load must stay under capacity, with continuous loads under 80% (1,920 W). In practice, kitchens, bathrooms and laundry rooms have their own circuit requirements, and good practice on a general circuit is around 10–13 outlets. What matters is what you plug in: thirteen phone chargers are nothing; three space heaters trip the breaker.

What happens if I exceed 80% of a breaker's rating?

For short bursts, usually nothing — breakers are designed to carry moderate overloads for a while before the thermal element trips. Sustained operation above 80% heats the wiring in the walls, which degrades insulation over time and is the fire risk the rule exists to prevent. A breaker that trips repeatedly under normal use is telling you the circuit is undersized for the load, not that the breaker is faulty.

Does a 240 V circuit handle twice the watts of a 120 V circuit at the same amps?

Yes. Watts equal amps times volts, so a 20 A, 240 V circuit handles 4,800 W versus 2,400 W for a 20 A, 120 V circuit — and 3,840 W versus 1,920 W at the 80% continuous limit. This is why large loads like dryers and water heaters use 240 V: double the power delivery at the same breaker size and wire gauge.