What's the average amount of food you should give to a blue nose pitbull?

I have 3 month blue nose pitbull and I don't know how much food I should give him. I feed him 1 cup of Purina puppy chow and occasionally canned dog food. He seems to be getting skinnier. Thanks for the help.

One cup of dog food doesn't nearly cut it for a medium sized puppy. Especially not 1 cup of Purina, which is one of the lowest quality foods you can find and is mostly fillers. They are growing rapidly and need a lot of calories. He should be getting more like 3 cups or more daily at that age, split into three evenly spaced feedings during the day. (so a cup in the AM, cup at lunch, cup at night). Since you've basically been feeding him starvation rations, you'll probably want to aim for more than 3 cups- probably more like 3.5 or 4 cups a day for now. Increase as necessary to maintain an appropriate weight as he gets larger.