Predicting Adult Size of a Lab

Question
We have a four month old yellow lab.  He ways about 36-37 pounds.  Curious if there is a rule of thumb - like he will likely double at adult weight, or something along those lines.  We had a 90 pound rescued lab previously, so I am curious if this boy will be that large...?

Answer
No way.  That is about the size of Xanthe, my female Lab.  My guess is he will top out at about 50 pounds if he is kept lean.  Of course, Labs are a hard headed lot, and may not pay any attention to what other Labs do.  

For a long, active life, not only keep him lean, but switch to adult chow now to slow growth and give his joints a chance to develop under less stress.   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