Start out with a 1/2 to 3/4 cup 3 times a day. If his poop gets soft you can decrease just a bit. If his poop is hard then increase a bit. It's a fine line there and that's how we judge how much food to feed. Every pup is a little different. Plus like you said leave water down for him 24/7 as they need plenty of fresh water too. Hope this helps.