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While some breeders may use the term "teacup" to describe individual Chihuahuas that are able to fit into a teacup as young puppies, it is important to know that there is no official size designation for teacups within the American Kennel Club's breed standards. All Chihuahuas are classified in the AKC's Toy Group and should not exceed 6 pounds, or roughly 5 to 8 inches in height.
Because individuals may vary greatly in size even within a litter, using the size of the parents to predict a puppy's full adult size is unreliable. Often a litter will include a much smaller puppy, or runt, which may or may not remain smaller than average. The Chihuahua Club of America cautions dog owners that because a smaller dog is often desirable, many breeders will use misleading size labels to inflate the sale price of a small puppy. Be aware that small Chihuahuas are not officially labeled with size guarantees, and may require special care due to their smaller stature.