How to Determine What Size Breaker Box I Need | Hunker Residential main breaker panels are available in four sizes, 100 amps, 125 amps, 150 amps and 200 amps. Round up your total amperage number to the nearest panel size. 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.