Amp Breaker Max Wattage Calculator: How Many Watts Can Breakers Handle?

With every amp breaker, it is useful to know how many watts they can handle. We are talking about maximum allowable wattage (using 80% NEC rule for continuous loads).

To help you figure out max wattage of any amp breaker, we have prepared these 2 key resources:

1. Amp Breaker Max Wattage Calculator. Here, you just insert the amp breaker size and voltage, and you will get the maximum wattage. Example: 15A breaker on 120V voltage has a maximum wattage of 1,440 watts.
2. Amp Breaker Max Wattage Chart. We list max. wattage for all standard amp breaker sizes at 120V and 220V voltages, namely 15A, 20A, 25A, 30A, 35A, 40A, 45A, 50A, 60A, 70A, 80A, 90A, 100A, 110A, 125A, 150A, 175A, 200A, 225A, 250A, 300A, 350A, 400A breakers.

We will also show you how to calculate max. wattage manually with a formula. Let’s start with the calculator and then look at the all-encompassing chart (super helpful for quick look-up):

Here’s how you can use this calculator:

Let’s say you have a 30A breaker on standard 120V voltage. You would like to know what is the maximum wattage this breaker can handle. Just pick ’30A’ breaker, and insert ‘120’ in the voltage field, and you get the result in this form (screenshot):

You can immediately see that 30A max wattage at 120V is 2,880 watts.

We did calculations for all standard breaker sizes and summarized the results in a chart, but let’s first explain how to calculate how many watts can an amp breaker handle:

How Many Watts Can Amp Breakers Handle?

The max. wattage amp breaker can handle depends on only 2 things, namely:

• Amp breaker capacity (15A, 20A, 30A, 40A, etc.).
• Voltage (usually 100-120V or 220-240V).

The one thing we need to keep in mind is the 80% NEC rule for amp breakers. This rule says that, for continuous loads, you can put only 80% of the amp breaker capacity on the breaker itself.

Example: A 20A amp breaker cannot handle 20 amps. Rather, it can handle 80% of that; that’s 16 amps.

Here is a formula for maximum wattage amp breaker can handle:

Max. Wattage = Amp Breaker Capacity × Voltage × 0.8

To calculate the amp breaker max wattage, we need to multiply the amp breaker capacity by voltage. We also have to multiply this by 0.8 to account for the 80% NEC rule.

Example: How many watts can a 20 amp breaker handle when running on the standard 120V voltage?

We just insert 20A and 120V into the equation above like this:

Max. Wattage (20A Breaker) = 20A × 120V × 0.8 = 1,920 Watts

This is it; 20A breaker can handle up to 1,920 watts at 120V voltage.

Here is the full chart of the max wattage of all standard amp breakers at 120V and 220V:

Amp Breakers Max Wattage Chart

From this chart, we see that, at standard 120V voltage, the following common breakers can handle well over 1,000 watts:

• 15A breaker can handle up to 1,440 watts.
• 20A breaker can handle up to 1,920 watts.
• 30A breaker can handle up to 2,880 watts.

The biggest 400A breaker at 220V can handle north of 70kW (70,400 watts, to be exact).

We hope that using the max wattage amp breaker calculator and this chart helps you figure out how much power you can get from each amp breaker. If you need any help with the calculations, you can always send us a comment below, and we will give you a hand.