How to Tell When a Puppy Is Full Grown

Updated October 16, 2022
happy Jack Russell Terrier puppy

When do puppies stop growing? Sometimes it's difficult to judge. Many people follow the old adage that a puppy is automatically finished growing and maturing by the time they're 1-year-old, but this isn't always the case. Some dogs may not reach their adult size until they are close to 2 years old, whereas others might be full grown at 6-months-old. It's also important to make a distinction between the time that puppies reach their full, adult size and the time it takes them to mature.

When Do Dogs Stop Growing?

Most canines reach their full size by the time they are 12 to 18 months old, although it does take longer for some of the largest breeds to finish growing. Some breeds even reach a full frame within the first 6 months of life, although it takes longer for the rest of the body to catch up. While there isn't a single age at which all dogs reach full size, there are some general guidelines that vary based on breed size. Consider these guidelines to get a sense of when you can expect your puppy to stop growing.

Rottweiler mix puppy

Small Breeds

These pups tend to reach their full-sized framework between 6 and 8 months old, and they'll typically fill out to their full weight by 12 months old. Common small breed dogs are Boston Terriers, Jack Russell Terriers, Chihuahuas, and Pugs.

Medium Breeds

You can expect breeds that fall into this group to reach their full-sized framework between 12 and 15 months old, but they usually won't reach their full weight until they're closer to 18 months old. Example of a medium-sized dog breeds include the Airedale Terrier, Border Collie, Australian Shepherd, and the Standard Poodle.

Large Breeds

This group grows more slowly, and most large puppies won't reach their full-sized frame until 15 to 18 months old and their full adult weight until they're about 2 years old. German Shepherd Dogs, Labrador Retrievers, American Pit Bull Terrier, and Weimaraners are examples of large-breed dogs.

Giant Breeds

Very large dogs, such as Mastiffs, Great Pyrenees, Saint Bernards, and Newfoundlands, take the longest to reach full size. Their basic framework is in place by about 18 months old, but it can take until age 2 or 3 for them to reach full weight and muscle mass.

Saint Bernard Dog

How to Estimate Your Dog's Full Grown Size

While you can get a general idea of how large your dog will be based on their breed, it becomes a bit harder with mixed breeds. Many breeds also have a range of sizes, and an adult's size will vary depending on whether they are male or female.

Puppy Size Calculator

One way to estimate their size is to use an online puppy size calculator. The Goody Pet offers an online calculator that requests you answer five key questions to determine the estimated size of your dog. Most other calculators will request similar information, including breed, date of birth, current weight, when the weight was recorded, and your dog's gender. Keep in mind that these will only give you an approximate guess and not a 100 percent accurate size and weight.

Growth Rate

Another way to determine their size is based on the age as a puppy. In general, most dogs are at 60 percent of their adult height by the time they are 4 months old. Puppies experience the largest growth rate from birth to about 6 months of age.

Weight Chart

It's a bit more difficult determining weight, as the same 4-month-old puppy will only be about 30 percent of their adult weight. You can use a puppy weight chart to estimate how heavy they will be based on where they fall in the weight range for their age. This involves tracking your puppy's weight over the course of several weeks or more if necessary.

Mixed Breeds

With mixed breeds, you'll have to do some more guesswork by comparing their weight at their age to another breed with a similar weight. It helps to know their breed heritage, if at all possible. There is an online calculator available for mixed breeds as well if you have a general idea of what breeds your dog is. Simply enter the mix of breeds and continue the requested steps. Keep in mind, this is only an estimate based on the breeds you have entered, so it will be approximate.

Different Breeds Mature at Different Rates

Size isn't the only consideration that determines when a dog will stop being a puppy. From a maturity perspective, it's important to keep in mind that different breeds tend to mature at different rates. Many people believe they'll only have to put up with rambunctious puppy behavior for a year. While some dogs do reach maturity near the end of their first year of life, others take significantly longer to mature.

For example, Border Collies and other herding dogs don't begin behaving like grown-ups until they are approximately 2 years old. Goldendoodles are one of the designer breeds that take the longest to fully mature, completing their growth at around two to two-and-a-half years. Catahoula dogs don't fully mature until they are closer to 3 years of age. On the other hand, Toy Poodles, Bichon Frises, and Shih Tzus typically behave like mature adults by the time they are 12 to 15 months old.

If you're bringing home a dog breed that takes a bit longer to mature than most, it's important that you are mentally prepared to live with an adult-sized dog who continues to behave like a puppy for an extended time. Doing your research prior to choosing a breed is important due to this aspect. Being prepared to handle a puppy for one year is much different than being prepared for a dog still acting like a puppy after two. Be certain you are ready to spend the extra time training and exercising a dog that takes longer to mature.

Signs a Pup Is Maturing

If you have been living with a puppy for a while and are waiting for them to settle down a bit, you've probably wondered how long it will take them to "grow up." While most dogs remain playful throughout their lives, there is a big difference between the lively activity of a mature canine and the boundless exuberance and dicey judgment exhibited by most puppies.

Labrador sitting grass

How you train your puppy, and how much socialization they receive, can all play into how quickly they calm down. Behavior is not always a reliable judge of maturation. There are markers that often indicate your dog is developing adult behaviors. For example:

  • A puppy tends to run at you full tilt and jump on you in greeting. A mature adult dog will be happy to see you, but is far less likely to bowl you over just to say hello.
  • Puppies may experience some trouble with house training, whereas adult dogs have fully developed bladders and increased bladder control.
  • Puppies are incessantly curious and tend to chew everything they can get their mouths around. In contrast, a dog that has matured past the puppy stage might have the occasional chewing incident, but this will become a rare event rather than the norm.
  • Puppies are full of energy and tend to demand a lot of attention from their owners. When dogs start to mature, they become calmer and no longer demand quite so much attention. A mature dog is happy to have your company, but they are also fine spending some time on their own.

If your pup has always seemed to take great joy in shredding newspaper, chewing your furniture or digging holes in your yard, watch for signs that these behaviors are starting to subside. This can be a signal that maturity isn't too far off. When you notice that your dog starts to exercise a little more restraint, it's a safe bet that they are starting to mature.

Research Your Breed

Before you get a puppy, be sure to find out how large they are likely to be when fully grown. Depending on how quickly your new pet grows, you may be in for quite a shock. Many people think about how much fun it will be to have a cute and cuddly puppy, but don't really stop to consider what it's like to live with a fully grown, adult dog. Breed profiles offer information on the size each breed will reach; check that out so there won't be any surprises. To find out how long a particular breed takes to mature, you'll need to speak with an experienced breeder.

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How to Tell When a Puppy Is Full Grown