The Chihuahua and the Toy Rat Terrier are easy to confuse as they share similar heights, weights and physical traits. However, the Toy Rat Terrier is a muscular dog, and the Chihuahua is not.
The easiest way to distinguish between a Toy Rat Terrier and a Chihuahua is to look at their bodies. Toy Rat Terrier should weigh between 4 to 6 pounds and be approximately 8 inches high. Chihuahuas should weigh between 2 to 6 pounds and should be approximately 6 to 9 inches high. Toy Rat Terriers, however, are notable for their musculature. They should have strong shoulders, a solid neck, a deep chest and strong legs. The body is compact but powerful. Chihuahuas, on the other hand, are less muscular; they are distinguished by their wide eyes, erect ears and long bodies.
The two types of dogs also differ in temperament. Toy Rat Terriers are affectionate, friendly and good with strangers. They are highly social dogs, and they are good with children. While Chihuahuas can be trained to be friendly and sociable, they are more territorial than Toy Rat Terriers. They are sometimes suspicious of people other than their owner, and they are not recommended for people with children.
Go to a reputable rat terrier breeder and you won't have to worry about it