Kibbles do vary, but so does your dog's caloric requirements when they're growing or very active. I have used several different brands, and usually start with the amount listed on the bag and then adjust based on the dog's appearance. When my dog was growing fast, between 6 and 9 months, she was eating 6 or even 7 cups of kibble and still had bones showing! Now that she's fully grown she's back to 3.5 cups.
It's not the size of the dog in the fight, it's the size of the fight in the dog. Mark Twain