There is no one-size-fits-all answer to this question, as the size of breaker you'll need for an electric car charger will depend on a number of factors, including the voltage and amperage of the charger, the length of the charging cable, and the type of vehicle being charged.   However, as a general rule of thumb, you'll need a breaker that can handle at least 30 amps for a standard Level 2 charger, and up to 50 amps for a faster Level 3 charger.