I agree with other posters here, if you do not know the lines from which you dogs come from and how they grow, then it is very hard to predict their adult weight. For instance Copper's breeder told me exactly how big he should be, but he was charting to be much smaller. She also told me that her lines tend to have a few later growth spurts. well low and behold he had a 15month growth spurt
which put him right where she said he would be.
Maddie's breeder told me that her lines tend to stop growing sooner, Maddie has only gained 5oz in the 3months that I have had her. She was charting slightly larger than she is now. at 7 months she is 2lbs and 6oz. I still expect her to gain some. But she is not following what the charts would have said at 12 weeks. I don't feel like you can go completly off of the parents weight either you have to look further back. Mad's Parents were 4-6lbs. but there were a few boys on the smaller side further back in the line.