So glad you joined our growing family of Yorkie Lovers
It is very difficult to determine adult weight. Like Rachel said, there are many growth charts on line - but their accuracy leaves much to be desired.
That being said, the few litters that my bitches produced have all followed the growth charts rather closely - with one huge exception - and that was little ButterBean who just stopped growing at 2.75 lbs. Butter is healthy - as a pup his forever mom and I had Butter tested every which way to determine if he had health issues, but there were none. He is definitely NOT fragile either - he lives on a farm and his favorite activity is chasing the chickens who dare to invade the backyard. Butter does have to be proected because he just doesn't understand the concept of being small of stature.