I think it varies so much on weight!
Our Yorkie Poo Crosley weighed about 3.4 when we got her at 12 weeks and she's like 16-17lbs now!
She is on a diet though and needs to shave off a couple!
Our neighbor has a Yorkie and he weighed 3 or 4 lbs at 12 weeks and I think he's like 13 or 14 lb now!