Enter the adjusted wattage into the calculator and the source voltage into the calculator to determine the circuit breaker amperage size.

Circuit Breaker Sizer Formula

The following formula is used to calculate the proper amperage size of a circuit breaker. 

A = P / V
  • Where A is the amperage the circuit breaker needs to be rated for (amps)
  • P is the adjusted power (wattage)
  • V is the source voltage (volts). The source voltage is commonly 240V for standard outlets.

To calculate the proper circuit breaker size, divide the adjusted power by the source voltage.

Circuit Breaker Definition

What is a circuit breaker?

A circuit breaker is a device that stops the flow of current in an electrical circuit if a certain current level is exceeded.

For example, if a circuit breaker is rated for a current of 1000 amps, and the current reaches 1005, then the circuit breaker should cut off all current to the system.

Example Problem

How to calculate circuit breaker size?

First, determine the adjusted power needed for the application. For this example, the adjusted power is found to be 100 watts.

Next, determine the source voltage. In this case, the source voltage is found to be 50 Volts.

Finally, calculate the proper circuit breaker size using the formula above:

A = P / V

A = 100/50

A = 2 amps.

This circuit breaker should be rated for 2 amps.