Small dog resting on a teddy bear

From Pint-Size to Full-Size: When Do Dogs Stop Growing?

Most dogs reach their full height at 18 months and their full weight at 2 years. Small purebred dogs, on the other hand, may stop growing between 6 and 8 months, and medium purebred dogs reach their full height and weight between 8 and 12 months.

Giant breeds like the Saint Bernard and the Great Dane take twelve to eighteen months or longer to reach their mature size. In general, the larger the dog, the longer the growth period. Small dogs also become sexually mature sooner than large dogs, so make sure your vet visits are up to date, and your dog is neutered at the proper time relative to its breed and size.

If your dog is a mixed breed or a rescue pup, the real question that may be troubling you is, “How big is this dog going to get, anyway?” With a purebred puppy, your breeder can give you a good idea of how big your dog will get and how long it will take to reach its full size. With shelter puppies, you’ll hear lots of different opinions, but in the end, you will have to wait and see.

Paw size is not always a useful measure with mixed pups since the paws can be quite large on a puppy but become proportionately smaller as the puppy grows into a dog. If you know the pups’ parentage, you can hazard a guess about how big it might get, but often only the mother dog is a known quantity. Even when you absolutely know the mixed puppy’s parentage, you won’t know if it will take after its mother or father until it lives with you a bit and grows into itself.

Determining When Your Mixed Breed Dog Will Stop Growing

A short-coated brown white puppy with a mother

When you take home a mixed breed puppy, you get used to people guessing which breeds your dog likely is. These people have one thing in common: They are all guessing. Your vet may be able to share an informed opinion based on the puppy’s looks and size when you bring it in.

You can also use a simple math formula. Divide your puppy’s weight by its age in weeks to determine its growth rate. Say your puppy is 8 weeks old and weighs 8 pounds. Divide 8 (pounds) by 8 (weeks), and you get 1 pound. Your puppy is growing at a rate of 1 pound per week.

Now multiply your puppy’s growth rate (1 pound per week) by fifty-two (the number of weeks in a year), and you get fifty-two pounds as your dog’s approximate adult weight. A fifty-two-pound dog is a medium/large dog, a nice average size. Your actual dog may be slightly larger or smaller, but this formula will give you an idea, at least.

Another way to determine your mixed-breed dog’s adult weight is to ask your vet if your puppy looks to be a small, medium, or large animal. If your puppy is little, multiply its weight at 6 weeks by 4 to get its adult weight. For medium dogs, multiply the puppy’s weight at 14 weeks by 2.5. For large dogs, double your puppy’s weight at six months to get its adult weight.

Keep in mind that female dogs tend to be smaller and weigh less than male dogs of the same breed. If you know your mixed-breed dog’s parentage, you might imagine that the puppy’s adult size might mirror the same-sex parent’s size, but that would be wrong. A mixed-breed dog can take after its father or mother or both no matter what their relative sizes.

What about height? Once you have a general idea of how much your adult dog is likely to weigh, you can consult a growth chart for breeds that look similar to get an idea of how tall your pup will be once it grows into an adult dig. All of these methods will give you an idea about adult size but not a guarantee. For every rule, there are exceptions.

Exceptions and Rules About Dog Size

A brown Belgian a Malinois puppy

Gracie, a mixed breed lab mix puppy, was adopted from a litter born to a medium-sized generic brown mother dog (about fifty pounds) and a tall purebred black lab father dog (about eighty pounds or so). A reasonable expectation might be that Gracie would not grow any bigger than eighty pounds, but she would likely be smaller than that, being female. She was black like her father, but the puppies in the litter were all different colors.

At 8 weeks, Gracie weighed about 8 pounds. Today, at 6 six years of age, she is one-hundred twenty-five pounds of muscle and brain and almost as tall as a giant breed, much taller and larger than her father. She looks like a black lab, only gigantic.

How can such a thing happen? Such things happen because one of the parent dogs was a mix of many different dogs, which made guessing the adult size of her puppies more of a gambling enterprise than a science. Who knows which gene switched on and made her who she is?

Marco, a male purebred miniature rat terrier, should have reached between 9 and 24 pounds. At 9 years of age, he weighs 5 pounds soaking wet. Is he really a rat terrier, or perhaps a toy rat terrier? Or even something else altogether? He’s charming, and no one cares.

If your puppy’s growth pattern seems truly aberrant, you can have the vet check the puppy over. If it is a purebred dog and is not keeping pace with breed standards, and if that matters to you because you meant to show the dog or it just matters to you, most reputable breeders will take the dog back and find you another.

If your puppy is a mixed breed, the story is quite different. Chances are you will take what you get and love the animal anyway. Still, if it genuinely grows beyond the limits of your capability to care for it, you can probably get help adopting the dog out from a local rescue organization.

Even purebred dogs experience variation within breed standards and sometimes beyond. Some less than scrupulous breeders have capitalized on this fact to create ‘giant’ breeds out of dogs that are not supposed to be giant, such as giant Malamutes. On the other extreme, unscrupulous breeders will breed down to create ‘teacup’ dogs.

Breeding for size can cause large dogs to develop problems like hip dysplasia, cranial cruciate ligament weakness, or heart and breathing issues. Breeding dogs tinier and tinier can make them prone to luxating patellas (knee caps that disengage when they walk) and increase deformities of all sorts.

Variation in adult dog size is normal, but breeding for size alone can create health problems in dogs that don’t need to be there. It is never a good idea to make size the primary consideration when selecting a purebred dog. Look for a licensed breeder instead who will match you to a pup most likely to agree with your own temperament and household.

When Size Is A Sign of Illness

Short-coated brown puppies

If your small dog is at least 1 year old, or your medium to large dog is at least 2 years old, and the dog suddenly begins to rapidly gain or lose weight, a visit to the vet is in order. Rapid weight gain or weight loss in dogs can be a sign of serious illness. This especially applies if the dog has become lethargic, is off its food, or seems to be in pain.

Problems that cause weight gain or loss in adult dogs include diabetes, Lyme disease, tumors, worms and parasites, and liver or digestive issues. Sometimes people overfeed their dogs, thinking they are being generous, not realizing that obesity in dogs can cause severe problems with their hips and joints.

Your adult dog should have a waist when viewed from behind, and you should be able to see its muscles but, in most cases, not its ribs. Usually, attentive owners will notice other dog problems long before they realize the dog’s weight has changed.

If your dog is merely obese from overeating, your vet can coach you on the when, what, and how much to feed him. Dogs are good scammers and can make you think they are starving when really they are fine. Owners have to set limits on treats and avoid feeding table scraps and not let the dog get the idea it can set its own table.

Some high protein dog foods are pitched to human beings based on human appetites and standards, yet not all dogs thrive on high protein food. Depending on your dog’s breed and temperament, it may do better on a lower calorie food with some grain in it. Some breeds gain weight more easily than others.

So When Will My Dog Stop Growing?

Your dog will stop growing somewhere between 6 months and 1 and a half years of age. If your dog is a mixed breed, you may get a surprise at the end, and you may not. Whatever size your puppy finally attains as an adult dog, treating your new friend with love and good care ensures it will be a long-lasting and happy part of your family.
"If you think dogs can’t count, try putting three dog biscuits in your pocket and then give him only two of them."
--Phil Pastoret

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