Usually you should feed your snake a rat that is as big a round as the thickest part or your snake. Once they are big enough for a small rat you can usually stay with 1 small rat once every 7-10 days for the rest of it's life since they don't need the same amount of food intake as they do when they are babies and growing. You will only need to go to medium rats if you end up with a large female.

Sent from my SAMSUNG-SM-G891A using Tapatalk