How the calculator works
Puppies don't grow at a steady rate, and small breeds finish growing sooner than large ones. The calculator uses growth data from 368,547 healthy dogs that were weighed at the vet as puppies and again as adults (18 to 24 months). For each size of dog and each week of age, we measured what share of their adult weight puppies had typically reached. Your puppy's weight divided by that share gives the estimate.
The data comes from a published study by the WALTHAM Centre for Pet Nutrition and the University of Liverpool, which built growth charts from the vet records of dogs that stayed at an ideal body condition throughout their first three years. The researchers released the underlying data openly, which lets us turn their growth standards into a calculator. Choose a breed and we use its typical adult weight range to pick the right size group and to show whether your puppy is tracking within it.
How accurate is it?
We tested the method on dogs it hadn't seen: the curves were built from half the dogs and checked against the real adult weights of the other half. The likely range shown contained the real adult weight for 8 in 10 dogs at every age. Estimates get much more precise as a puppy gets older.
| Puppy's age | Typical error | 8 in 10 estimates within |
|---|---|---|
| 8 weeks | 18% | 37% |
| 12 weeks | 16% | 30% |
| 16 weeks | 13% | 26% |
| 20 weeks | 11% | 23% |
| 26 weeks (6 months) | 10% | 21% |
| 39 weeks (9 months) | 8% | 15% |
| 52 weeks (12 months) | 7% | 14% |
In other words, for a 12-week estimate of 10 kg, half of dogs end up within about 1.6 kg of that and 8 in 10 within about 3 kg. Re-check every month or so for a sharper answer.
Puppy growth chart by size
How much of their adult weight typical healthy puppies have reached at each age (median):
| Adult size | 3 months | 4 months | 6 months | 9 months | 12 months |
|---|---|---|---|---|---|
| Toy (under 6.5 kg) | 42% | 54% | 75% | 88% | 93% |
| Small (6.5–9 kg) | 41% | 54% | 76% | 90% | 94% |
| Small to medium (9–15 kg) | 36% | 49% | 72% | 87% | 92% |
| Medium to large (15–30 kg) | 31% | 45% | 71% | 89% | 95% |
| Large (30–40 kg) | 31% | 44% | 69% | 88% | 94% |
| Very large (over 40 kg) | 26% | 39% | 65% | 86% | 94% |
The pattern is clear: at three months a toy puppy is already around 42% of its adult weight, while a very large puppy is about a quarter of the way there. By six months most puppies are 65–76% grown.
When do puppies stop growing?
In this data, typical puppies reached 90% of their adult weight at about 9 to 10 months and 95% at about 12 to 14 months, then filled out slowly after that. Because "adult" here means the weight at 18 to 24 months, very large and giant breeds may keep gaining for longer than the calculator shows.
Healthy growth matters more than size
- Watch shape, not just the scales. A puppy can be on track for size and still be carrying extra weight. Your vet can show you how to check body condition at home.
- Feed for the expected adult size. Many puppy foods have separate small- and large-breed formulas. Ask your vet which suits your dog.
- Crossbreeds vary more. For mixes like Cavoodles, the parents' adult sizes are the best guide. Our Toy Cavoodle guide and generations explainer explain why.
- Sudden changes are worth a vet visit. Weight loss, stalled growth or rapid gain can all have medical causes.
Puppy growth FAQs
How can I tell how big my puppy will get?
Use your puppy's current age and weight with the calculator above, and if you know them, check the parents' adult weights. For crossbreeds and rescue dogs of unknown mix, the calculator's range is a sensible guide.
Is it true a puppy doubles its 4-month weight?
It depends on size. In this data, toy and small puppies were typically about 54% of adult weight at four months, so they end up a little under double. Medium and large puppies were about 45%, so a little over double, and very large puppies about 39%, so roughly two and a half times their four-month weight.
Why is my puppy heavier than the breed average?
Breeds vary, males are often larger than females, and many dogs are crosses. If your puppy is above the typical range, ask your vet to check body condition before assuming it will simply be a big dog.
Does the calculator work for mixed breeds?
Yes. Choose "Mixed or not sure" and pick the adult size you expect, or the size of the larger parent if you know it. Mixed breeds vary more, so treat the range as more useful than the single number.
Is my data saved?
We don't save your puppy's weight. The calculation runs in your browser. Like the rest of the site, we count anonymous usage in Google Analytics (the size group, breed and age used) to improve the tool.
Still choosing a dog? Our free dog breed quiz matches more than 200 breeds to your home, routine and the size of dog you want.
Sources and data credit
Growth curves derived by RightDogMatch from: Salt C, Morris PJ, German AJ, Wilson D, Lund EM, Cole TJ, Butterwick RF (2017). Growth standard charts for monitoring bodyweight in dogs of different sizes. PLOS ONE 12(9): e0182064. Supporting data: University of Liverpool Research Data Catalogue, dataset 377, licensed under CC BY 4.0. Our analysis: healthy purebred dogs in ideal body condition with an adult weight recorded at 18–24 months, grouped by breed adult weight; weekly medians and 10th–90th percentiles, smoothed. The original data come from primary-care veterinary records in the United States (1994–2013). This calculator is general information, not veterinary advice.