This isn't something you have to guess at.

Weigh the snake regularly. Is it gaining a lot of weight? If it's an adult, and hasn't just come out of breeding, then you are feeding it too much. Is it losing weight? You are not feeding it enough. If it's barely gaining weight, just a little bit, then you are feeding it the right amount of food.

No need for guessing at how much energy it's using, or how much food it needs--just weigh it.