By the time a large breed puppy is old enough for 2 meals a day, a cup will be way too little. I am getting a 7 week old Lab Sunday. It will be getting 1/2 cup each of 3 times a day. By the time it is 3 months old and we cut back to 2 meals a day, it will be getting 3-4 cups a day. Any recommendation is only a starting point. If it is less than 4 months, you should be feeding a puppy chow now. Switching to an adult chow for the
larger breeds at 4 months, slows growth and helps develop sturdier joints. Adult chows vary. Don't feed a puppy one with more than 1.5% calcium.
Your dog definitely should be narrower at the waist than the hips and chest. You
should be able to easily feel the ribs, but not see them. Each dog is different.
Standard recommendations are a good place to start, but each dog must have its
food and exercise adjusted to its individual needs. Here is a link to a good
illustrated guide,
http://www.longliveyourdog.com/twoplus/RateYourDog.aspx