Proper Puppy Feeding Amounts

I probably can't tell whether the amount of food is right for your dog, but if he's not fat or thin, it's probably a good amount. However, I would recommend that you might want to check out some other foods for him.  Purina Pro Plan is not really a high quality food. If you look at the first few ingredients, Pro Plan tends to have things like corn gluten meal, poultry by product meal, ground wheat, etc. I'm hoping someone can come along and provide some better info here. But, higher quality foods tend to be cheaper many times than some foods that appear to be cheaper. This is because these higher quality foods tend to have more calories per cup, so you feed less than if you are feeding a low quality food.

http://www.dogfoodadvisor.com/choosing-dog-food/karen-becker-choose-dog-food-2/

I usually go by how the pup looks.  If he's not looking too chubby or too thin, I'd stick with that amount.  I tend to keep pups and adults more toward the thin side but not to the point where their hip bones and backbone are prominent. One sign of overfeeding is loose stools so if you see that you might want to cut back a little.  His food requirements are higher as he's growing and you may find you will feed him less when he's full grown. 

 I guess 2 cups twice a day sounds good. I had a puppy around 6 months back and I use to feed him a total of 3 cups a day. If your puppy is eating it completely without any problem then it is good and he will become healthy, of course.