You need to go by the guidelines printed on the food packaging. The amount you should feed for size and age should be printed on the package. Puppies are in high growth, so the total food for the day should be split into 3 meals. I can't tell you the approximate amount for a pitbull pup as my dogs were different sizes. I read the dog food package to find out the right amount. A dog that's being fed the right amount should be hungry at the beginning of each meal and finish all that's given. If it's not finished, put it in storage after 15 minutes and hold it for the next mealtime.