How to Know What Size Your Puppy Will Be

What size the puppy you're thinking about adopting will grow up to be is almost the first question future adopters ask. That's normal, since size will determine not just housing, but also all kinds of expenses.

You should know it's not possible to determine with total certainty the adult size of a mixed-breed puppy, a cross of who-knows-how-many dogs. But we can look at certain aspects that'll help us estimate the animal's final size.

Canine Growth Phase

Every dog grows very quickly during the first months of life. Roughly until 4-6 months old, this growth is more pronounced. After that, it continues on average until twelve months, but at a slower pace. Also, keep in mind these timeframes will vary depending on the dog's size.

Smaller-sized dogs reach maturity sooner and, as a result, also stop growing sooner. This is the exact opposite of what happens with large or giant dogs, which can extend their growth phase until 18-24 months. Medium-sized dogs, for their part, more or less follow the timeline mentioned of 4-6 and 12 months.

If it's a purebred dog, it's easy to know when it's reached the end of its growth, since there's a standard for each dog breed that gives us a fairly accurate idea of its adult size. It'll also be easier to estimate if we know the mother and father.

Identifying Size Based on the Puppy's Family

Looking at the puppy's family that we might know, like the mother or the rest of the litter, can sometimes help give us a general idea of its adult size. But it's not an exact science. We stress this because some owners look at the mother and assume the puppy will be the same size once grown.

But that's not true. A 10 kg female could give birth to a litter with individuals that, as adults, exceed 20 kg, depending on who she was bred with. In fact, the same litter can include puppies ranging from 9 to 20 kg. Knowing the father doesn't guarantee accuracy either.

A cross between a small female and a large male can result in puppies of intermediate size, but also smaller or larger ones — all within the same litter. In conclusion, it's not always easy to determine a mixed-breed dog's size. There's quite a margin of error.

Figuring Out Size Based on Puppies' Paws

Another widespread belief is that puppies with big, wide paws will be large-sized when grown. Well, that's not true either. They won't end up Chihuahua-sized, but they might turn out more Cocker Spaniel-sized than German Shepherd-sized. So, if we only look at the paws, we might be in for a surprise a few months later.

A Puppy's Size and Weight Will Indicate Its Adult Size

Keeping track of a puppy's weight is actually a good way to get an idea of its adult size. Even at birth, there'll be a weight and size difference between, say, Great Dane puppies and Shih Tzu puppies. In medium-sized breeds, it won't be as obvious, but it's also not as important when the uncertainty is only between weighing 15 or 18 kg.

We can ask our vet or check canine growth charts to track the puppy's progress and estimate what adult size it's heading toward. As a reference, a six-month-old puppy of a medium breed has practically reached its final size, though it'll still gain weight.

At four months old, on average, it'll be at half this size, so we can simply double it to estimate its final weight. Height is considered the same, meaning half the adult size around four months old. So, the key is tracking its weight, its growth pattern, and also how its growth rate slows down.

Calculating Size Based on a Puppy's Age

If we're going to factor in the puppy's age to assess its current and future growth, we obviously need to know this information. This isn't always easy. We often adopt puppies rescued from abandonment whose birth date we don't know. Luckily, this information is easier to obtain.

During the first weeks of life, developmental milestones like opening their eyes, losing the umbilical cord, or walking allow for a fairly accurate estimate. Our vet or people experienced in raising dogs can help us. After that, it's possible to look at dental characteristics:

1. The first teeth appear at 2-3 weeks old.
2. Then canines and premolars come in. The last premolar is dated to around eight weeks old. There can be significant variations — for example, in large breeds, teeth usually come in faster.
3. Puppies don't have molars.
4. These baby, or deciduous, teeth only stay in place for 3-7 months.
5. The incisors fall out first, around three months.
6. Permanent canines, premolars, and molars appear between 4-7 months.
7. In conclusion, a 7-8 month old puppy will already have its permanent set of teeth.