AKC has put Yorkshire Terrier in it's list of 21 toy breeds. Chihuahua comes very closer to Yorkshires and their average weight is even less than Yorkshire's average weight of 7 Lbs.
Maltese and Pomeranian also have very similar weight ranges as Yorkshires. Yorkies have an average height of 8-9 inches. For Maltese, average height is around 8-10 inches while Pomeranian stands at 7-12 inches.
Though, there are other dog breeds which have more average weight as compared to Yorkshire Terriers. Papilion is bigger with average weight of 7-10lbs.
Also, a good number of Pet Yorkies have an average weight of more than 7 Lbs. More than 60% of dog owners believe that their Yorkie's weight is more than 7Lbs.
It is really important to Crate train your Yorkie to assure that he grows really well and well mannered as well. You should learn from my Experience as well.