From what others have said, the best plan is to feed once every five to ten days and to feed more per feeding if he needs more. However, I don't know whether they take into account that you are feeding live. I think it might be tough for a snake to take two, live, adult mice in one sitting.
The frozen mice that I buy from PetCo weigh about 20 to 25 grams each. If I were feeding a snake as big as yours, I'd feed him two f/t of this size. I guess if he's taking three per week, then you can keep up the current plan. Tosha says that 10 to 20 percent of body weight once per week is the formula for feeding mice that are smaller than the snake's diameter. If he takes three of these per week, he's getting around 20% of his body weight.
I think most people weigh immediately after a snake defecates. That weight should represent the most snake and the least food. I tend to weigh as often as I can regardless of defecation cycle. I don't expect any one number to be the "right" weight, but I get a feel for the trend. As long as the overall trend is upward, I'm happy.
Bill
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It's not how many snakes you have. It's how happy and healthy you can keep them.