Most bodybuilders just GUESS as to what is the precise amount of rest days between workouts. In my opinion, this is wrong. If you are serious about bodybuilding and muscle growth, you must be as precise as possible, and leaving guessing to the bodybuilders who don't understand sound bodybuilding principles.
With that said, you MUST track your progess each and every workout in order to determine if you have the ideal, or precise amount of rest. If you are gaining strength with each workout, rest time is idea. If you are staying the same, or losing strength, rest time needs to be increased. Some bodybuilders need up to 7 or more days rest between workouts to fully recover.
Another Tip - Rest days are directly proportional to the intesity of your bodybuilding exercise.
To help those on this forum I have put together a Free Report on the 5 Biggest Bodybuilding Mistakes. You can download it at mistakes .
I hope this helps!