How Big Will My Puppy Get?

By Ruthie Bently

When people decide to adopt a puppy, they usually want to know how big it will be when full grown. Interestingly enough, the genes that determine a puppy’s adult size come from both the sire and the dam, not just one parent. They each contribute three alleles of size to their offspring and the combination of these determines how large your puppy will be. However, without knowing which alleles for size each parent is providing, it can be difficult to determine the puppy’s adult size.

If you get a puppy from a reputable breeder and are getting an AKC recognized breed, ask the breeder if both parents are on the property and if you can see them. By looking at the sire and dam of your chosen puppy, you can get an idea of how large it will be as an adult. An alternative is to check your local library for the American Kennel Club’s latest edition of The Complete Dog Book. It contains the breed standards of dogs currently recognized by the AKC. It can provide you with the adult size and weight that your puppy should be when  full grown.

If you are adopting a mixed breed puppy, it can be a bit more difficult to determine its adult size. Not everyone owns both the sire and the dam of a mixed breed puppy. Many times the female will come into season and become pregnant before her owner knows what has happened, and they don’t always know the male or males responsible. If you are adopting a puppy from a shelter, they may not know the breed of either parent or the age of the puppy. If you can see both of the parents, you can get an idea of the size the puppy will be when full grown. If both the parents are seventy pounds, chances are your puppy will be close to that size full grown. Likewise, if you have two ten pound parents your puppy will be a smaller adult.

I read an article which stated that with two dogs of differing sizes, the puppy’s size will come more from the mother. I disagree with that; I personally know of several dogs whose father was larger than the mother and the puppy is a large adult. One dog I know is a fifty pound cockapoo/terrier mix whose mother was a cockapoo that weighed ten pounds and whose father was a terrier mix that was over sixty pounds.

There are several other ways to help you determine the size that your adorable puppy will grow to. Look at their paws – if they have large paws it is a safe bet they will be a large dog when they are full grown. How loose is their skin? If they aren’t a Shar Pei it is another indicator that they will be growing into that extra skin and could be a large dog.

You can also document the puppy’s weight and height as it grows, and by keeping track of this on a growth chart you might be able to estimate how large your puppy will be as an adult. If the age of the puppy is unknown you could have your vet examine their teeth to help determine their age. The growth plates of a puppy’s long bones (found in their legs) fuse closed between the age of eight to eleven months old, but their weight continues until they are adults. A large breed puppy like a Saint Bernard or Great Dane will not be fully grown before the age of two.

An easy way to predict your puppy’s adult height is that it will reach approximately 75% of its adult height at about six months old. A non-scientific method is called the “double it” formula. You take the puppy’s weight at fourteen weeks and by doubling this you can get the estimated weight it will be as an adult. Since many of the larger breeds are not adults until the age of two, this formula won’t work for them.

Whichever method you choose, make sure before you get a new puppy that they will be a welcome addition to your family. A dog can bring great joy, unconditional love and plenty of laughter to your household, but you need to remember they will be with you for a long time. So now that you know how big your puppy will be, how big of a puppy do you want?

Read more articles by Ruthie Bently