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What Size Breaker Do I Need for 1800 Watts?

Written by Edwin Jones / Fact checked by Andrew Wright

what size breaker do i need for 1800 watts

If you want to know the answer to “What size breaker do I need for 1800 watts?”, you’ll need a minimum 20 amp breaker for a standard 120-volt circuit. However, properly sizing a breaker requires some calculations and considerations to ensure safety and prevent tripping.

Are you still feeling confused? Read on to find out more about how to calculate the correct size for breakers.

Calculating Breaker Size for 1800 Watts


How did we know the recommended size breaker for 1800 watts is 20 amps? Here’s our calculation process:

  • First, determine the voltage. Most homes operate on 120 volts. With 120 volts, we can use the basic equation for appliances below:

\[\text{Amps} = \frac{\text{Watts}}{\text{Volts}}\]

\[{Amps} = \frac{1800 \text{ watts}}{120 \text{ volts}} = 15 \text{ (amps)}\]

So at 120V, 1800 watts require 15 amps.

  • However, breakers aren’t sized for the exact load. They’re designed to allow continuous operation at 80% of the rating to prevent overheating. So, with a 15 amp load, we would need:

\[\frac{15 \text{ amps}}{0.8} = 18.75 \text{ amps}\]

Since the National Electrical Code (NEC) recommends rounding up to the next standard size. Rounding up, the next full size is 20 amps.

  • Therefore, an 1800-watt device running at 120 volts will require a 20-amp breaker.

1. For 240V Circuits

What if you have a 240V circuit instead? Simple. We perform the same calculation and just adjust the voltage figures:

\[\frac{1800 \text{ watts}}{240 \text{ volts}} = 7.5 \text{ amps}\]

\[\frac{5 \text{ amps}}{0.8} = 9.375 \text{ amps}\]

  • Round up to the next size, 10 amps.
  • So at 240 volts, a 10 amp breaker can support 1800 watts.

Clearly, higher voltage allows a smaller breaker for the same wattage. However, as pointed above, most household circuits in the USA operate at 120 volts.

2. For 12V

If operating an 1800 watt appliance at 12V DC, such as in an off-grid solar system, the calculation would be:

\[\frac{1800 \text{ watts}}{12 \text{ volts}} = 150 \text{ amps}\]

  • Accounting for the 80% continuous load rule,

\[\frac{150 \text{ amps}}{0.8} = 187.5 \text{ amps}\]

  • Rounding up to the next standard size, you would need a 200 amp breaker for 1800 watts at 12 volts DC.

Thick expensive cables are required to handle the large DC amp loads. It’s important to run these types of wattage calculations when designing a 12V DC electrical system.

3. Wire Gauge

When sizing the breaker, also consider the wire gauge. The conductors must be sized appropriately to handle the amperage without overheating.

For a 20 amp, 120-volt circuit, the code requires a minimum of 12 AWG copper wires. If the wires are too small for the amp load, they’ll pose a fire hazard.

4. Safety Factors

Don’t size a breaker purely on the wattage alone.

  • Add an extra margin beyond the minimum required. A 30 amp or even 40 amp breaker may be justified for a 1800W device to allow for inrush current and prevent nuisance tripping.
  • For continuous loads like refrigerators and AC units, leave a wider extra margin to account for unexpected incidents, such as electrical surges.
  • If the circuit has other outlets, raise the breaker’s size further to account for additional loads.
  • Use a high-quality brand breaker less prone to nuisance tripping.


When sizing a breaker for 1800 watts, choose at least 20 amps at 120 volts after using a calculator and safety considerations. Use thick 12 AWG wire for the circuit. Allow an extra margin beyond the minimum required for safety.

Follow the NEC guidelines, and when in doubt, go higher on the breaker rating to prevent tripping and ensure reliable operation. With smart planning, you can safely run 1800-watt devices on standard household electrical circuits.

We hope our article has helped you learn the answer to “What size breaker do I need for 1800 watts.”

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