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					Originally Posted by doglover4  So, apparently he's 2 lbs at 6 weeks. Doing the "double at 6 weeks and double again" rule I found, he'd be 8 lbs I guess. But both his parents are 4.5-5 lbs. A puppy can grow to be almost double his parents' weight?
 And yes, I really do want a smaller dog- 10 lbs would be too much for me.
 
 Obviously health and temperament are most important, but meeting the breeder and a few of her dogs, I have no concerns there.
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  Yes, a Yorkie can grow much larger than the parents.  The gene pool that determines size can go many generations back.  Sometimes a tiny pops up in a litter, sometimes a large one pops up in a litter.  My boys (brothers from different litters) are bigger than their parents and bigger than their littermates.   
The only way to guarantee size is to buy an adult.  Otherwise, as KazzyK wrote, it is an educated guess as to what size the puppy will mature to.