I bump up feeder size when needed. When what I am feeding is no longer a lump in the snake I will usually look at going up a size.....unless they are adult snakes on maintenance. This will be different in each situation.

If a person feeds their snake every five days while you are doing every seven they will probably jump up a size before you. Or maybe your snake eats every week while another's eats every two weeks and is giving them fits, your snake will be the one that most likely jumps up a size first. You just don't know what is going to happen......especially with a Ball. My Ball once went six months with only a small rat during that time. She was fine and just being a Ball but she did it. So during that time if another's Ball is still eating every week they are going to pass mine up. See the variables?

If you want to try a rat a rat pup is probably the right size.