When is a dog fully grown? The answer depends on its size: a toy or small dog is usually fully grown at about 9 to 12 months, a medium dog at about 12 months, a large dog at 12 to 18 months, and a giant dog at 18 months to 2 years. Those are guides, not hard lines: a dog grows fast in its first year, then slows down, and it may fill out — gaining muscle and breadth — for months after it has stopped growing taller. This guide gives the growth ages by size, what 'fully grown' means, and when to switch from young to adult food. Every figure is a guide, because individual dogs vary. The puppy weight predictor estimates adult weight from a puppy's current weight and age.
The short version is: small breeds finish growing first, large breeds last, and a dog is fully grown when it has reached its adult height and weight — which is not the same as being an adult. A dog that has stopped growing still needs training, socialisation, and care, and it should not be switched to adult food until it has finished growing, or it may not get the nutrients it needs. The puppy growth chart by size guide gives the growth shares by age, and the when is a dog considered a senior guide gives the senior thresholds by size.
When is a dog fully grown
The table below gives the age at which a dog of each size is usually fully grown, with the typical adult weight for that size. Use it to know when to expect your dog to stop growing — and when to switch from young to adult food.
| Size | Fully grown at | Typical adult weight |
|---|---|---|
| Toy | 9–12 months | 1–5 kg |
| Small | 9–12 months | 5–10 kg |
| Medium | About 12 months | 10–25 kg |
| Large | 12–18 months | 25–40 kg |
| Giant | 18 months–2 years | 40–90 kg |
Read the table from top to bottom and the pattern is clear: the smaller the dog, the sooner it finishes growing. A toy dog is usually fully grown at 9 to 12 months, while a giant dog is usually fully grown at 18 months to 2 years. A cat is usually fully grown at about 12 months, but a large breed such as the Maine Coon can keep growing until it is 2 to 4 years old. The dog age calculator works out the human-age equivalent for any age.
What 'fully grown' means
'Fully grown' means a dog has reached its adult height and weight — but it does not mean it has stopped changing. A dog that has stopped growing taller may still fill out, gaining muscle and breadth, for months afterwards, and it may still be maturing in behaviour: a dog that is fully grown at 12 months may still be an adolescent in behaviour until it is 18 months or 2 years old. A dog that is fully grown should be switched to adult food, but it still needs training, socialisation, and exercise.
A dog grows fastest in its first few months: a puppy is about a fifth to a quarter of its adult weight at 8 weeks, about half at 6 months, and about four-fifths or more at 12 months, when small breeds are near-adult and large breeds are still growing. The puppy weight chart by age guide gives the growth shares by age, and the puppy age calculator by weeks guide gives the development at each age.
When to switch from young to adult food
Switch from young to adult food when your dog has finished growing: at about 9 to 12 months for a small breed, about 12 months for a medium breed, 12 to 18 months for a large breed, and 18 months to 2 years for a giant breed. For cats, switch at about 12 months, or later for a large breed such as the Maine Coon. Switch gradually, over a week: mix the new food with the old, increasing the new food a little each day, so the stomach has time to adjust.
Do not switch too early: a puppy that is switched to adult food before it has finished growing may not get the nutrients it needs, and it may grow more slowly or less well. Do not switch too late, either: an adult dog that is still eating young food will get too many calories, and it may gain weight. The puppy feeding schedule by age guide gives the feeding schedule from weaning to adulthood, and the dog food calculator works out the daily calories for any weight and stage.
Growth by breed
Growth varies by breed as well as by size: a breed that is large for its size will grow for longer than a breed that is small for its size, and a breed with a heavy frame will fill out for longer than a breed with a light frame. A dog that is a crossbreed will grow at a pace between its parents' breeds, and its adult weight will be between theirs — so a crossbreed's growth is harder to predict, and the ranges on this site are typical estimates, not guarantees for any one dog.
To judge your own dog's growth, weigh it every two weeks as a young animal, and write the result down: a single reading matters less than the line over weeks. A puppy that is gaining weight steadily is growing well; a puppy that is not gaining weight at all over two weeks, or that is losing weight, needs a vet check. The dog growth chart by breed guide gives the growth ages breed by breed, and the puppy weight predictor estimates adult weight from a puppy's current weight and age.
When to ask a vet about growth
Ask a vet if your puppy is not gaining weight at all over two weeks, if it is losing weight, if it is growing much faster or much slower than expected for its breed, or if it is limping, stiff, or in pain. A puppy that grows too fast can develop joint problems, especially in large breeds, and a puppy that grows too slowly may have a health problem. A vet can work out whether the growth is normal, and what to do about it.
Ask your vet, too, about when to switch from young to adult food: the ages above are guides, and your vet may move them earlier or later depending on your individual dog's breed, its weight, and its health. A dog that is overweight should be switched earlier, and a dog that is underweight should be switched later. The how much food should a puppy eat guide gives the calorie tables for young dogs.
For related reading, see the puppy weight predictor, the puppy growth chart by size guide, the puppy weight chart by age guide, the puppy age calculator by weeks guide, the dog growth chart by breed guide, the puppy feeding schedule by age guide.
Frequently asked questions
When is a dog fully grown?
A toy or small dog is usually fully grown at about 9 to 12 months, a medium dog at about 12 months, a large dog at 12 to 18 months, and a giant dog at 18 months to 2 years. Those are guides, not hard lines.
When should I switch from puppy food to adult food?
Switch when your dog has finished growing: at about 9 to 12 months for a small breed, about 12 months for a medium breed, 12 to 18 months for a large breed, and 18 months to 2 years for a giant breed. For cats, switch at about 12 months, or later for a large breed such as the Maine Coon. Switch gradually, over a week.
Does 'fully grown' mean my dog is an adult?
Not quite — a dog that has stopped growing taller may still fill out for months afterwards, and it may still be an adolescent in behaviour until it is 18 months or 2 years old. A dog that is fully grown should be switched to adult food, but it still needs training, socialisation, and exercise.
How fast does a puppy grow?
A puppy grows fastest in its first few months: it is about a fifth to a quarter of its adult weight at 8 weeks, about half at 6 months, and about four-fifths or more at 12 months, when small breeds are near-adult and large breeds are still growing. Weigh it every two weeks, and write the result down.
How do I know if my puppy is growing well?
Weigh it every two weeks and write the result down: a puppy that is gaining weight steadily is growing well. A puppy that is not gaining weight at all over two weeks, or that is losing weight, needs a vet check. The line over weeks matters more than any single reading.
When should I ask a vet about growth?
Ask a vet if your puppy is not gaining weight at all over two weeks, if it is losing weight, if it is growing much faster or much slower than expected for its breed, or if it is limping, stiff, or in pain. A puppy that grows too fast can develop joint problems, especially in large breeds.
Results on this page are estimates for general information only and are not veterinary advice. If your pet is ill, underweight, overweight, pregnant, or has a health condition, consult your veterinarian before changing diet or care.