A 15 amp breaker handles up to 1,800 watts at full capacity

A 15 amp breaker is rated for 15 amperes at 120 volts, which equals 1,800 watts. This comes from the basic electrical formula: watts = amps × volts. In a standard US home, most outlets on a 15 amp circuit run at 120 volts, so 15 × 120 = 1,800 watts total.

However, you should not run a 15 amp circuit continuously at 1,800 watts. Electrical code requires that you limit continuous loads to 80 percent of the breaker's capacity. That means the safe ongoing load is 1,440 watts (15 amps × 120 volts × 0.80). Breakers trip when you exceed their rating, cutting power to the entire circuit to prevent overheating and fire.

The difference between the full 1,800 watts and the safe 1,440 watts matters because many household devices run for hours at a time. A space heater drawing 1,500 watts continuously will eventually trip a 15 amp breaker, even though 1,500 is less than 1,800. The breaker gets hot from the sustained current and trips as a safety measure.

Key Takeaways

  • A 15 amp breaker at 120 volts can handle 1,800 watts at its absolute maximum, but only for short periods.
  • For devices that run continuously, the safe limit is 1,440 watts (80 percent of capacity), which is what electrical code requires.
  • If you plug too many devices into one 15 amp circuit, the breaker will trip and cut power to protect your home from overheating wires.
  • A 20 amp breaker handles 2,400 watts maximum and 1,920 watts continuously, making it better for high-draw appliances like microwaves or space heaters.

Why the 80 percent rule exists

Electrical wiring generates heat when current flows through it. The longer current flows, the hotter the wire gets. A breaker that trips at exactly its rated amperage would allow wires to run at dangerous temperatures during normal use. The 80 percent rule keeps wires cooler and gives the breaker room to handle brief spikes without tripping.

Think of it like a car engine. The engine can theoretically run at maximum RPM indefinitely, but doing so would destroy it. You drive at a sustainable speed most of the time and only push the engine hard when you need to. Electrical circuits work the same way.

Common devices and their wattage

Most household devices draw far less than 1,800 watts, so a 15 amp circuit can handle several at once—as long as they do not all run simultaneously. A typical laptop charger uses 60 to 100 watts. A desk lamp uses 10 to 60 watts. A computer monitor uses 20 to 40 watts. You can run all three together without any problem.

The trouble starts with high-draw appliances. A microwave uses 800 to 1,200 watts. A space heater uses 750 to 1,500 watts. A hair dryer uses 1,200 to 1,800 watts. If you plug a hair dryer and a microwave into the same 15 amp circuit and run them both, you will exceed 1,800 watts and trip the breaker when ready. If you run a space heater alone on a 15 amp circuit for several hours, the sustained 1,500-watt draw will eventually trip the breaker even though it is under the 1,800-watt maximum.

When you need a 20 amp breaker instead

A 20 amp breaker at 120 volts handles 2,400 watts maximum and 1,920 watts continuously. Kitchens and bathrooms are required by code to have 20 amp circuits for this reason—those rooms have the most high-draw appliances. A microwave, toaster, and coffee maker can all run on the same 20 amp kitchen circuit without tripping it, whereas they would overload a 15 amp circuit.

If you find yourself constantly resetting a breaker in a particular room, or if you want to plug a space heater or hair dryer into a circuit that already has other devices, a 20 amp circuit is the solution. An electrician can upgrade the breaker and rewire the circuit in an hour or two, and the cost is usually between $150 and $300 depending on your area.

How to check what is on your circuit

Your breaker panel shows which outlets and fixtures each breaker controls. Open the panel door and look for a label or diagram inside. If there is no label, you can create one by turning off each breaker one at a time and noting which lights and outlets go dark. Write the results on a piece of tape and stick it inside the panel door for future reference.

Once you know what is on each circuit, add up the wattage of devices you plan to run at the same time. If the total approaches 1,440 watts on a 15 amp circuit, you are pushing the safe limit. If it exceeds that, you need either a 20 amp circuit or a different outlet on a different circuit.

What happens when you overload a breaker

A breaker trips by flipping its switch to the off position. You will see the switch in the middle or slightly toward the off side. To restore power, flip it all the way off first, then flip it back on. If it trips again when ready, you have a serious overload or a short circuit and should not keep resetting it—call an electrician instead.

Repeated tripping is a sign that the circuit is undersized for what you are trying to do. Ignoring it and using extension cords or power strips to plug in more devices is dangerous. Breakers exist to prevent fires. If a breaker keeps tripping, it is telling you that the circuit cannot safely handle your load.

240 volt circuits and larger breakers

Some appliances run on 240 volts instead of 120 volts. Electric dryers, electric ovens, air conditioning units, and water heaters all use 240 volts. A 30 amp breaker at 240 volts handles 7,200 watts (30 × 240). A 50 amp breaker at 240 volts handles 12,000 watts (50 × 240). These circuits are separate from your regular 120 volt outlets and have their own breakers in the panel.

You cannot plug a 240 volt appliance into a 120 volt outlet, and you cannot use a 240 volt circuit for regular household devices. The voltage and plug shape are different by design. If you are adding a new high-power appliance like a hot tub or a large air conditioning unit, an electrician will install a dedicated 240 volt circuit with the appropriate breaker size.

Frequently Asked Questions

Can I use a 20 amp breaker on a circuit that was originally 15 amps?

No. The wiring itself must be rated for 20 amps. Older homes often have 14 gauge wire on 15 amp circuits, which will overheat if a 20 amp breaker allows 20 amps to flow through it. An electrician must upgrade both the wire and the breaker. Swapping only the breaker is a fire hazard.

Why does my breaker trip when I use a space heater?

Space heaters draw 750 to 1,500 watts continuously. On a 15 amp circuit, the safe continuous limit is 1,440 watts. A high-setting space heater will eventually trip the breaker. Move it to a different circuit, use a lower heat setting, or have a 20 amp circuit installed in that room.

Is it safe to use a power strip to plug in more devices?

A power strip does not change the circuit's capacity. If you overload the circuit, the breaker will trip whether the devices are plugged directly into the outlet or into a power strip. Power strips are convenient but do not solve an undersized circuit problem.

What is the difference between a breaker and a fuse?

Older homes use fuses instead of breakers. A fuse is a one-time device that melts when overloaded and must be replaced. A breaker is reusable—it trips and can be reset. Both protect against overload, but breakers are safer and more convenient. Many electricians will upgrade a fuse panel to a breaker panel for around $1,500 to $3,000.

Can I plug my air conditioner into a 15 amp outlet?

Window air conditioners draw 500 to 1,500 watts depending on size and cooling power. A small unit might work on a 15 amp circuit if nothing else is plugged in, but a larger unit will trip the breaker. Check the nameplate on your unit for its wattage, add it to other devices on that circuit, and compare the total to 1,440 watts.