The American Kennel Club standard for the Chihuahua breed is that they should be almost square in appearance, although the standard tolerates a slightly longer body for the female dog for the purpose of reproduction. The most important part of the American Kennel Club standard for the Chihuahua is that the skull be apple shaped with a tail that is carried very high and being of moderate length.

When it comes to proportions the Chihuahua should be slightly greater in length than their height at the withers. In males especially it is highly desirable that the breed has an almost square body, but a slightly longer body is permitted in the female dogs for the purpose of reproduction. The temperament of a Chihuahua should be alert, quick, lively and very courageous. Overall the Chihuahua is described as a small, dainty, compact breed with a highly spirited intelligence while being neither snappy nor withdrawn in behavior.

The Chihuahua standard set by the American Kennel Club states that the head should be well rounded with an overall "apple dome" shape. They should have lean cheeks and jaws with a muzzle that is moderately short, slightly pointed and has a definite stop. Eyes should be large and round, but not protruding. The eyes should be set well apart with the center of the eye being on a plane with the lowest point of the ear.

The preferred eye color is dark or ruby, but eyes that are lighter in color may be permissible. The ears should be large and flaring with an angle of approximately forty-five degrees to add breadth between the ears. The jaw should be strong and have a scissor bite that is regular and complete. This means the upper teeth should closely overlap the lower teeth and be set square to the jaws. The dog's neck should be of medium length and with only a slight arch.

The Chihuahua should have steps that are long, springy, energetic and active while have both good reach and drive. When viewing from the back, the Chihuahua should have hind legs that move almost parallel to each other in order for the foot prints of the hind feet to fit directly into those of the front feet.

Most of the time the limbs will converge towards the center point of gravity and leave a single track when they increase their speed. The head should be raised and firm while the dog has a free and springy movement without visible effort. The desired coat for shorthaired dogs is glossy with a soft texture.

For shorthaired dogs the coat should be glossy with a soft texture. For the longhaired Chihuahua the coat should be fine, silky and smooth or slightly wavy. All shades and color combinations are allowed by the standard.

The ideal weight for a Chihuahua according to the standard is between 1.5 and 3 kg. Lighter weights are permitted but weights over 3 kg are disqualified.