Mine all doubled their 16 week weight, give or take 5 lbs., which is a rule of thumb. Sam was 55 lbs (freak of nature puppy) and Linus was 45 lbs. Sam has been as heavy as 110 (not exactly obese, but not lean) but I try to keep him in the upper 90s (he goes on a diet if he hits triple digits) and Linus, though he is just under 18 months, fluctuates between the high 80 and the mid 90s lbs, and I try to keep him closer to 90.
Sam's dad was 85 lbs and Linus' father was on the smaller side of conformation Labs at 75 lbs. Though parents are a good indicator, it's never been true for my dogs. The double the weight at four months rule of thumb (not claiming it's a hard rule, but it's a good indicator and can be right on for larger dogs) has always been true for me and everyone I know with larger dogs, unless, of course, they allowed them to get fat. Also, these were all well-cared for, healthy, rolly polly puppies, who had gotten off to a great start without illness, parasites, or injuries, etc.