Teddy weighed
3lbs@8 months and 3lbs 13oz at one year. I moved him from puppy food to adult food and he went up to 4lbs 5oz (on a fat day) in one month! He is still very lean and small. I would say that you really can't tell until they have moved on to adult food how big they will get because they lose their puppy fat from the puppy food and start to build muscle from the protein in the adult food.
That was my experience, anyway.