How Big Will My Dog Get? A Guide to Your Dog's Fully Grown Size

Posted by Petdirect on 3rd Jun 2026

Working out how big your dog will be when fully grown helps with all sorts of everyday choices, from the right size bed and harness to how much to feed them. It also helps you pick the right life stage food, since a small dog and a large dog reach each stage at different ages.

Here is how to get a good estimate, even while your puppy is still growing.

The quick version: your dog's breed is the best clue to their fully grown size, so check the typical weight band for their breed below. For a crossbreed, look at both parents and expect your dog to land somewhere between them, often closer to the larger one. As a rough guide, many puppies reach about half their adult weight by four to five months. Smaller dogs finish growing by around 10 to 12 months, while large and giant breeds can keep filling out until 18 to 24 months.

Start with the breed

The breed is the best clue you have. Most breeds have a fairly predictable fully grown weight, so if you know your dog's breed you are most of the way there. Have a look at the typical weight ranges further down this page to see where your dog is likely to land.

If your dog is a crossbreed, look at both parents. A good rule of thumb is that your dog will usually end up somewhere between the two, often closer to the larger parent. Your breeder is also a great person to ask, as they have seen how previous litters turned out.

A few rough guides while they are growing

None of these are exact, but they can help you picture where your puppy is heading.

Puppies that look like they have a bit of growing to do, with larger paws and a lankier frame, often still have growing left in them.
As a very rough guide, many puppies are around half of their fully grown weight by four to five months. This varies a lot by breed, so treat it as a ballpark only.
If you can see the parents or know how littermates turned out, that is one of the most reliable signs of all.

When do dogs stop growing?

Smaller dogs finish growing earlier, and bigger dogs keep going for longer.

Size group	Usually fully grown by
Toy and small breeds	Around 10 to 12 months
Medium breeds	Around 12 months
Large breeds	Often still filling out until 15 to 18 months
Giant breeds	Can keep growing until 18 to 24 months

This is why a large or giant breed dog can look fully grown in height well before they have finished filling out.

Typical fully grown weight ranges

These are the size bands we use in our pet life stage calculator. Every dog is an individual, so use these as a guide rather than a hard rule.

Size band	Fully grown weight	Breed examples
Toy	Under 5 kg	Chihuahua, Pomeranian, Toy Poodle, Maltese
Small	5 to 10 kg	Miniature Schnauzer, West Highland Terrier, Shih Tzu, Pug
Medium	10 to 25 kg	Border Collie, Cocker Spaniel, Staffordshire Bull Terrier, Beagle
Large	25 to 45 kg	Labrador Retriever, Golden Retriever, German Shepherd, Boxer
Giant	45 kg and over	Great Dane, Mastiff, Saint Bernard, Newfoundland

Feeding for your dog's size

Once you have a sense of how big your dog will get, you can match their food to it. Many ranges are tailored to small, medium, or large breeds, with kibble size and nutrition suited to how fast each group grows. Large and giant breed puppies in particular do best on a food formulated to support steady, controlled growth rather than rushing it.

Small breed puppies

Medium breed puppies

Large breed puppies

Gear they will grow into

Knowing the adult size ahead of time saves you buying twice. A crate or pen sized for the grown dog, with the space sectioned off while they are little, will last from puppy days onwards. For harnesses and beds, choose an adjustable or roomy option and check the fit regularly as your puppy fills out.

Why fully grown size matters

Knowing your dog's fully grown size helps you choose food, beds, crates, and harnesses that will still fit as they grow. It also affects when your dog moves into their senior years, since larger breeds tend to reach their senior stage earlier than smaller ones.

If you would like to check which life stage your dog is in now, our pet life stage calculator can help. Just choose their fully grown size and pop in their age.

Still not sure?

If you are unsure how big your dog will get, your breeder or your clinic can give you a more tailored estimate based on your dog's breed, frame, and growth so far. They can also let you know if your puppy is growing at a healthy rate.

Frequently asked questions

How can I tell how big my puppy will get?

Start with the breed, which gives you a typical fully grown weight band. For a crossbreed, look at both parents. As a rough guide, many puppies are about half their adult weight by four to five months, and pups with large paws and a lanky frame usually have more growing to do.

At what age do dogs stop growing?

It depends on size. Toy and small breeds are usually fully grown by around 10 to 12 months, medium breeds by about 12 months, large breeds by 15 to 18 months, and giant breeds can keep filling out until 18 to 24 months.

Will my crossbreed be bigger or smaller than its parents?

Most crossbreeds end up somewhere between their two parents, and often a little closer to the larger one. Seeing the parents, or knowing how earlier litters turned out, is one of the most reliable signs.

Does my puppy need large breed food?

If your dog will be a large or giant breed when grown, a large breed puppy food supports steady, controlled growth and is worth choosing. Smaller breeds suit small breed formulas with smaller kibble. The size bands above will help you pick the right match.