Yes, it matters how long the legs are. It's addressed in the Standard but in a round about way. Chihuahuas are supposed to be slightly off square, which means they will be a tad longer in body than they are tall at the withers. See the Body section of the Standard. The length of the leg should be in proportion to the length of the body as indicated above. In general, the heighth of the body is going to be equal to the length of the leg.
An example (just to illustrate, not actual measurements) - For a dog that is 8 inches tall at the withers, the break down should be about 4 inches from withers to bottom of chest and another 4 inches from elbow to foot giving the total of 8 inches at the withers. Then measuring from point of shoulder to rear point of croup, the dog should be about 9 inches long, giving that slightly longer than tall proportion.
Lisa M. Greene
dedicated to Chis for over 25 years
The smallest breed with the biggest heart.