The AKC standard for the Yorkshire Terrier used to state that the dog was to not exceed 7 pounds (3.17 kg). There was not any set minimum size.
This has changed. The AKC now has an official weight of 4 to 7 pounds (1.81 to 3.17 kg)
Before this change, breeders could produce a 2 pound puppy without causing any stirs. Now, most attempt to stay within the set breed standard. So, if this is the standard, what are tiny teacup Yorkies? A different breed? A variation? Let's look at the details all about Teacup Yorkies.