How to Estimate the Size of Puppies as Full Grown Dogs

Teeny tiny puppies are almost universally considered adorable. That's why there are so many videos and photos of puppies online. But every puppy will eventually grow up into a full grown dog and it can be hard to prepare for a dog in your home if you don't know how big it will grow up to be. While there are many ways to calculate the eventual size of your pup, using a dog size calculator online or doing some calculations on your own can at least give you some idea of how big your dog will be eventually.

2 months old dachshund puppy laying comfortably in hands of its owner
It is important to understand how big your puppy will grow when it is an adult.
credit: Alena Kravchenko/iStock/GettyImages

When do puppies grow up?

A common question people ask after adopting a puppy is "at what age is a puppy no longer a puppy?" The answer isn't as simple as it may sound though. Some dogs will be full grown adults at only six months old, while other dogs take up to two years to fully mature. While the specific ages will vary based on breed and even the individual in question, the general rule is that a small breed dog will grow up in less time than a large breed dog.

In other words, if your puppy is six months old, it might have nearly reached its full grown size if it is a tiny Yorkie, but if it's a large-breed dog such as a mastiff, it may still only weigh a fraction of its full adult weight.

Get to know the breed

One of the best places to start when trying to learn the eventual size of your dog is with the breed. Daily Dog Stuff says guessing a purebred's ultimate size is usually pretty simple, just look up a dog registry site such as those from the American Kennel Club. These will give you information both on the average size of the breed and whether there are large discrepancies between the size of males and females of the breed.

Guessing what the ultimate size and weight of a mixed breed dog will be can be a bit more of a challenge, but if you know what breed the parents are, you can usually estimate that your dog will be somewhere between the sizes of both parent's breeds. If you are trying to estimate what the size and weight will be of a mutt with unknown or mixed breed parents, you could always submit a sample of your dog's blood for a DNA test to get a better idea of what breeds make up your pup's ancestry.

Look at the parents

If you know the parents of the pup, this can also help to estimate the size of your future adult dog. If they're around the same size, girl puppies will usually end up around the size of their mother and males will usually end up closer to the size of the male parent. If the dogs are different sizes, your dog will almost certainly be somewhere between the two. When they're drastically different sizes, this can also make it difficult to tell how big the pup will grow to be.

If you only have the mom to go by, this can still give you some indication. If she's only 15 pounds, for instance, and your six-week-old pup is already almost 10 pounds, you can assume your pup will end up a lot bigger. On the other hand, if your pup is around 5 pounds, it might be closer to her weight.

Puppy weight estimator

If you don't know the puppy's breed and haven't seen its parents, there are more mathematical ways to guess its eventual weight. Vet Babble says if you at least know whether your pup is a small or toy breed versus a medium to large breed, you can use a simple calculation to find its weight, but you'll need to know its weight at siz or 14 weeks, respectively. A toy or small breed will grow to be around four times its weight at six weeks. For medium to large breeds, the dog will eventually be around 2.5 times its weight when it is 14 weeks old.

In other words, a toy poodle who weighs two pounds when it is six weeks old will grow to around eight pounds (two pounds times four) when it is an adult. On the other hand a 24 pound German Sheppard who is 14 weeks old will grow to be about 60 pounds (24 pounds times 2.5) eventually.

Other weight calculations

If you don't know what your small dog's weight was at six weeks or the large dog's weight at 14 weeks, you might want to look up an online puppy height and weight calculator or a puppy weight chart template. A puppy weight estimator tool will allow you to come up with the most accurate size estimate possible and you can find different calculators based on the information you have. Some will only look at the dog's weight and age, while others will allow you to enter other info for a more accurate answer, which could include whether your dog has been fixed yet, what his breed is, his gender, and his height.

If you want to do the math yourself, DogAppy says you can also take the current weight of your pup and divide it by how many weeks old he is. With this info you can find out his average weight per week and then multiply this by 52 (the number of weeks in a year) to find out what he could weigh after a year. In other words, if your dog is 10 weeks old and weighs 10 pounds, you would estimate that 10 pounds divided by 10 weeks is one pound a week so after 52 weeks, he would weigh around 52 pounds.

This method's accuracy will still vary based on his breed's size. So for it to be most accurate, you would want to perform this calculation at 12 weeks for a small-breed, 16 weeks for a medium-breed, or 20 weeks for a large-breed.

Other things to consider

As stated earlier, Fido Savvy points out there are other factors that may affect a dog's growth than simply her breed or weight at a certain age. Dogs that are neutered or spayed at a very young age may not grow as much as those who are fixed once they reach full adulthood. Gender will often affect a dog's weight, with female dogs usually weighing less than males.

Additionally, these weight estimates are all based on a dog being fed a healthy and age-appropriate diet. Obviously a malnourished puppy will grow up to weigh less than he probably should given his genes. But even a dog who is fed adequately could have growth issues; in fact, many large dogs can actually have their bones grow too rapidly if they are fed diets with too much protein, calories or calcium. This will not only make the dog larger than it should be, but it can result in bone and joint diseases later in life.