I have 3 Yorkies. All different weights, and sizes.
Rocky is small faced and short, but since he was neutered, he has put on weight. He is 6 1/2 pounds.(he use to weigh 5) He's fat in the middle. (9years old)
Rosie, who was my biggest, is now 6 pounds. 4years old. I don't like her to get too thin, because she looks funny for her head and body size.
Gracie is little 3lbs/9oz and she is 13 months old. She looks right for her size, but I have to watch out for her because she is so little.
Like everyone on here, Yorkies come in all shapes and sizes. But you love them all.