Beats me?? I wish I knew. I have a 6 mo female, Suzie who is 4 lbs, 11 oz. One vet told me she will be small, probably about 7 pounds. That was when she was 3 or 4 mos old. Her brother Cookie is 7 lbs, 3 oz. He is the longest cat I have seen and very tall, but very slim. I *think* he is going to be a large boy, but not that heavy. He had HUGE paws when he was little.
Zakk was 6 lbs at 6 mos, and is now 9 1/2 lbs, and at an ideal weight. Rocky was about 8 lbs at 6 mos, and is bigger than Zakk in length. He is now about 12 1/2 pounds, but is a little overweight. Just thought I'd throw that info out there.