amount of food

Question
I have a 7-month old black lab puppy.  I want to know when I should switch to adult food and at 7-months...how much and how often should I be feeding my dog?

Answer
Switch as soon as you can.  When you get down to about half a weeks worth of puppy chow, start mixing in a little adult until at the end of a week, it is all adult chow.  Switching to an adult chow for the larger breeds at 4- 6 months, slows growth and helps develop sturdier joints.

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 adjusted to its individual needs. Here is a link to a good illustrated guide,
http://www.longliveyourdog.com/twoplus/RateYourDog.aspx

Likely 3 cups a day is about right even if it would happily eat 2-3 times that much. Too much and too rich of a diet is the worst thing you can do for a growing puppy's joints.  One meal a day now would be fine if you want.