Canidae Feeding Rec's

This link goes to the feeding guidelines found on Canidae's webpage . . . I'm having some trouble though with what the recommend for puppies . . . I don't understand how a 10 pound puppy and a 25 pound puppy can be classified in the same feeding bracket?

Winston has been on Canidae for a couple weeks now and it has been going fine, but he seems to need more than what they recommend.  I want to make sure he's getting enough, but I don't want to over feed him.  Right now, he gets a heaping cup in the morning and evening, and about 1/4 cup at lunch just to tide him over (i tried doing even meals, but I ended up wasting a lot of food around lunch.

Is there another way to calculate how much food he needs?  Maybe based on calories or something?  Right now, he's 3 months and 21 lbs.  I'd say that he is modearately to very active.


[linkhttp://www.canidae.com/dogs/all_life_stages/dry.html]Canidae Feeding Guide[/link]