If you can't see a "food bump" in his tummy after 24 hours, it's time to move up to the next size of prey. Like bitsy said, the Munson plan is an excellent guide. (Here it is, from Roy Munson's Serpent Lounge forum)
The Munson Plan (Sample Feeding Chart): Revised 06/08/08
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-When they're on single pinks (2-3g), I feed every 5-6 days. (Snake = 4-15g)
-Double pinks (3g x 2) every 5-6 days. (Snake = 16-23g)
-Small fuzzies (5-7g) every 6-7 days. (Snake = 24-30g)
-Regular fuzzies (7-9g) every 6-7 days (Snake = 30-50g)
-Hoppers (9-12g) every 6-7 days (Snake = 51-90g)
-Weaned (14-20g) every 7 days (Snake = 91-170g)
-Adult (20-30g) every 7-x days (Snake = 170+) See below.
Note: Adult females are fed more frequently than adult males (especially following brumation). Adult females are fed every 7-12 days; adult males are fed every 11-14 days.
This is by no means scientific, and not all corns will cooperate 100% with the schedule. The weight ranges I gave for the prey and snakes are approximate.
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If you don't have a scale, you judge the proper prey size by the girth of your snake. Food items should be about 1.25-1.5 times the width of the snake's body at its widest point. If you happen to have a supply of smaller food items on hand when it's time to move up in size, it's perfectly fine to double up on the smaller ones until they're gone.