All Yorkies are classified by being in the "Toy Group". This does not mean they are going to be tiny, just that they are a small breed dog. It's just a classification. Chihuahuas, maltese, and pug are also toy breed dogs. Yorkies can be a range of different sizes, usually between 4-7 lbs.
https://www.akc.org/breeds/yorkshire_terrier/index.cfm