how big will he be?

Question
I have a 4 month old male black lab who is not yet neutered. He already weighs 35 pounds and most people tell me that he is going to be a very big dog. He is being fed the recommended amount and is in very healthy condition. I was wondering, based on his age and weight now, what his final size will be as long as he is consistently fed the correct amount of food?

Answer
That is very hard to say, my guess not real big, 50-60 pounds.  Check the ends of the leg bones.  If they are still much knobbier than an adult's, the growth plates are still open and it is still growing.  If not, do not expect much more growth.

You may find this link interesting,   http://jn.nutrition.org/cgi/content/full/134/8/2027S

Switching to an adult chow for the larger breeds at 4 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 and exercise adjusted to its individual needs. Here is a link to a good illustrated guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx