How to Determine What Size Breaker Box I Need | Hunker The size of your breaker box tells you how many electrical appliances or fixtures can run at the same time. If you live in an all-electric home, you will need a larger breaker panel than if the structure used a combination of electricity and gas. Your needs also depend on the types of appliances you use. Breaker Panel Sizing - Buyer's Inspection Service Breaker Panel Sizing. The main disconnect fuses or breakers act as safety barriers in the case of an electrical problem or overload. The most common sizes in residential use are 100 amps, 150 amps and 200 amps. The amperage (amps) referred to is a measurement of electricity. The higher the number of amps, the more electricity you can use in your home.