To shed some light on size in the canine is difficult. Most measurements of size show continuous variation from one extreme to the other. This research was conducted on crossing various tall breeds with various short-legged breeds. The results were misleading and inconclusive. What was proven though is that in the same population a wide range can occur in the F2 generation from parents contrasting greatly in some quantitative character. Even in a litter of 7 dogs, there were extremes in height and size. This shows nicely the wide a range must be due to many genes interacting. The many genes that influence the expression of some polygenic trait do not necessarily all exert the equal effects on that trait. Some may enhance it, others reduce it. It is the variability among such genes that provides the material for selection. Put more simply, it allows the breeder to select for bigger or smaller dogs, as he prefers. Apart from polygenic inheritance, in some species single genes have been identified which exert an altogether disproportionate effect on size. Hereditary dwarfism caused by a single gene occurs in the dog, and it would be interesting to see to what extent (if any) the smaller breeds of dogs have been made small by the single genes that override the usual determination of body size by a complex of polygenes. Body size in dogs is limited to some extent by the size of the dam. Chihuahua bitches will not produce offspring that will become as big as Great Danes. This maternal limitation of ultimate size is found in other mammals. That limitation is not caused by the mothers genes it is a restriction imposed by the prenatal environment, which cannot be entirely overcome after the animal is born. All we really know for sure is that:

1. All domestic dogs descend from the wolf,
2. Genetic information including that for size is passed on to every generation
3. The size of dogs is polygenic in inheritance
4. Prenatal and postnatal environmental factors influence size
5. There can be a large variation from one extreme in the breed to the other in a single litter.

Some individuals weigh 8, 10 pounds, (or even more). Some years ago, it was customary to breed an oversized female to a very tiny male, for safer whelping. This produced a mixture of very small (and desirable) pups and very large (and undesirable) pups. Thus, genes for various sizes became fixed in the breed.

For a healthy and sturdy Chihuahua, we recommend 4 pounds and up.

How can you tell how big a puppy will grow up to be?

The bad news is: You can't for sure.

The good news is: You can estimate, using several guidelines.

Adult size in Chihuahuas, as far as weight goes can be reasonably accurately assessed by trying the following:

Predicting adult weight:

The double-it formula:

Whatever a puppy weighs at 14 weeks, double it to get the adult weight, give or take half a pound. So if you're looking for a 4 to 6 pound adult, look for a 14-week-old puppy who weighs 2 to 3 pounds.

This useful weight chart holds true for many Chihuahuas.
 
 

For a 4 to 6 pound adult, look for these puppy weights:
 

10 weeks	1 lb. 9 oz to 2 lb. 6 oz
12 weeks	1 lb. 14 oz to 2 lb. 13 oz
14 weeks	2 lb. 2 oz to 3 lb. 3 oz
16 weeks	2 lb. 7 oz to 3 lb. 11 oz

Not every breeding line can be predicted by the Double-It Formula or Chihuahua weights guideline above. A few lines (and individuals) stay small for awhile, then suddenly spurt in growth. Other lines (and individuals) start out big but never grow much more. Knowledgeable breeders should be able to estimate the mature size of their puppies.

The parents' size:

This guideline is also not very accurate, because some big parents can have tiny puppies, while some small parents may produce a giant. But generally, if both parents are less than six pounds (and are good representatives of the breed), their puppies are more likely to be, of similar size and conformation. If they are both oversized, your puppy is likely to be, too. It helps to know the background size for at least 5 generations.

TIP: Buy a good electronic scale. Double-check it against the scale at your post office by weighing a package on your scale, then asking the P.O. to weigh the same package. If yours is off, at least you will know by how much. Then weigh the pups on this and only this scale each time as outlined above. And no, the puppy is not going to keep all four feet on the scale. Weigh it in a box, then subtract the weight of the box.

Height:

It is funny, but height is seldom mentioned in our breed. Usually they are about 6 to 9 inches from the ground to the top of their shoulders.

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