How Many Watts Can a 15, 20, 30 or 50 Amp Circuit Handle?
Part of the project planners: Planning to frame and finish a wall and Sizing a circuit: watts, amps, wire and breaker.
A circuit's limit in watts is its breaker rating times the voltage: a 15 amp circuit at 120 volts handles 1,800 watts, and a 20 amp circuit 2,400 watts. For a load that runs three hours or more, keep it to 80%: 1,440 and 1,920 watts. The circuit capacity calculator does the sum for any breaker and appliance.
Watts by breaker size
| Breaker | 120 V maximum | 120 V continuous (80%) | 240 V maximum | 240 V continuous (80%) |
|---|---|---|---|---|
| 15 A | 1,800 W | 1,440 W | 3,600 W | 2,880 W |
| 20 A | 2,400 W | 1,920 W | 4,800 W | 3,840 W |
| 30 A | 3,600 W | 2,880 W | 7,200 W | 5,760 W |
| 40 A | 4,800 W | 3,840 W | 9,600 W | 7,680 W |
| 50 A | 6,000 W | 4,800 W | 12,000 W | 9,600 W |
| 60 A | 7,200 W | 5,760 W | 14,400 W | 11,520 W |
| 100 A | 12,000 W | 9,600 W | 24,000 W | 19,200 W |
| 200 A | 24,000 W | 19,200 W | 48,000 W | 38,400 W |
How many devices on one circuit?
At the 80% continuous limit, for a 120 V circuit:
| Device | Watts | On a 15 A circuit | On a 20 A circuit |
|---|---|---|---|
| Space heater | 1,500 W | 0 | 1 |
| Hair dryer | 1,800 W | 0 | 1 |
| Microwave | 1,100 W | 1 | 1 |
| Toaster | 1,200 W | 1 | 1 |
| Vacuum cleaner | 1,000 W | 1 | 1 |
| 10 W LED bulb | 10 W | 144 | 192 |
| 60 W incandescent bulb | 60 W | 24 | 32 |
| Laptop charger | 65 W | 22 | 29 |
A typical space heater, hair dryer or toaster is about 1,500 watts, so a 15 amp circuit can run only one of them, and it should have nothing else on it. Many outlets and lights share one breaker, so add everything up.
The 80% rule
A breaker is meant to carry its rated current for a short time, but a continuous load (one that runs for three hours or more, such as lighting, a heater on a thermostat, or an EV charger) should not exceed 80% of the breaker rating. A 20 amp breaker should carry 16 amps, which is 1,920 watts at 120 volts.
Wire for each breaker
The wire must be rated for at least the breaker. Typical copper sizes at 75°C:
| Breaker | Copper wire |
|---|---|
| 15 A | 14 AWG |
| 20 A | 12 AWG |
| 30 A | 10 AWG |
| 40 A | 8 AWG |
| 50 A | 8 AWG |
| 60 A | 6 AWG |
See the wire size calculator for the exact size with a long run and the voltage drop.
What to do if a breaker trips
- Unplug the devices and reset it. If it trips again with nothing plugged in, there may be a fault: call an electrician.
- If it trips only with a heater or other big load, the circuit is overloaded: use a different circuit, or reduce the load.
- Never replace a breaker with a larger one, or tape it shut. The breaker protects the wire from overheating.
- If you need more power, add a circuit. That is a job for an electrician.
Electrical work can start fires and cause serious injury or death. Use this for planning and learning, follow your local electrical code, and have a licensed electrician do or inspect household wiring.
Frequently asked questions
How many watts can a 15 amp circuit handle?
1,800 watts at 120 volts as a maximum, and 1,440 watts for a load that runs continuously (the 80% rule).
How many watts can a 20 amp circuit handle?
2,400 watts at 120 volts, and 1,920 watts continuously. At 240 volts it is 4,800 watts.
How many watts can a 30 amp circuit handle?
3,600 watts at 120 volts or 7,200 watts at 240 volts, and 80% of that continuously.
How many watts can a 50 amp circuit handle?
12,000 watts at 240 volts, and 9,600 watts continuously.
Can I run two space heaters on one circuit?
No. A 1,500 W heater takes 12.5 amps, so two need 25 amps, more than a 15 or 20 amp circuit can carry. Even one heater is over the 1,440 W continuous limit of a 15 amp circuit.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.