The Russian toy is the smallest breed of dog on average, and ranges in weight from 3 to 6 pounds and 8 to 10 inches in height. Toy fox terriers are a close seconds, with an average weight between 3 1/2 to 9 pounds.
The Russian toy was originally bred for hunting rats, and comes in both short and long coated varieties. There is no difference in size between these coat types. Toy fox terriers are extremely athletic as well, and originate from full-sized fox terriers. Some Chihuahuas may be smaller than either Russian toys and toy fox terriers, and have an average height between 4 to 6 inches.