Puppy Size Predictor
Estimate how big your puppy will get
Likely full-grown by about 12 months.
📊 Estimate based on standard puppy growth-rate projection. Your vet and the parents' size are the best guides.
How to predict how big your dog will get
No method is perfect, but a few together give a good estimate:
- The parents' size is the single best predictor. If you can find out the mother's weight, you are most of the way there.
- Growth-rate projection, which the calculator above uses: current weight divided by age in weeks, times 52. Most accurate from about 14 to 20 weeks.
- The breed. A purebred has a well-known adult range; look it up and the calculator should land near it.
- The “half-by” rule. Medium-breed puppies are roughly half their adult weight by 4 to 5 months. Double the weight at that age for a quick check.
When do puppies stop growing? (chart by size)
Bigger dogs grow for longer. Here is roughly when each size reaches half and full adult weight.
| Size | Adult weight | Half-grown by | Full-grown by |
|---|---|---|---|
| Toy / Small | under 25 lbs | ~3.5 months | 8–12 months |
| Medium | 25–50 lbs | ~4.5 months | ~12 months |
| Large | 50–90 lbs | ~5 months | 15–18 months |
| Giant | 90+ lbs | ~5.5 months | 18–24 months |
Estimating a mixed-breed puppy's size
Mixed-breed puppies are the hardest to call, which is exactly why this tool is useful. With no papers, lean on the growth-rate estimate above, the size of the mother if the shelter or foster knows it, and oversized paws as a loose hint that more growing is coming. A DNA test gives the most certainty if you really want to know.
Most rescue puppies are listed with an estimated adult size for this reason. Browse adoptable puppies and dogs across Canada to find one whose expected size fits your home.
Bigger dog, bigger budget
Adult size is not just a fun fact — it drives cost and care. Large and giant breeds eat far more, need bigger doses of preventives, and generally have shorter lifespans. Before committing to a breed, it is worth knowing the numbers:
- See the lifetime difference with our dog cost calculator.
- See how size affects aging and lifespan with our dog age calculator.
Frequently asked questions
How big will my dog get?
The most reliable clues are the parents’ size and the breed, but you can also estimate from your puppy’s current growth rate. A common formula projects adult weight as your puppy’s current weight divided by its age in weeks, multiplied by 52, which is what the calculator above uses. Estimates are most accurate from about 14 to 20 weeks. For mixed breeds with unknown parents, the calculator is your best quick guide.
When do puppies stop growing?
It depends on size. Small and toy breeds reach their adult size by about 8 to 12 months. Medium breeds finish around 12 months. Large breeds keep filling out until 15 to 18 months, and giant breeds like great danes and mastiffs are not fully grown until 18 to 24 months, even though they reach most of their height earlier. They gain bulk and chest depth well after they stop getting taller.
How accurate is a puppy weight calculator?
It is a solid estimate, not a guarantee. Growth-rate projection works well for purebred and medium-sized puppies between about 14 and 20 weeks. It is less reliable for very young puppies (under 12 weeks), giant breeds (whose growth curve is long and uneven), and mixed breeds where the parents’ sizes are unknown. Treat the result as a useful ballpark and confirm with your vet, who can read your puppy’s frame and paws.
Can paw size tell you how big a dog will get?
It is a rough hint, not a measurement. Puppies with paws that look oversized for their body often still have growing to do, which suggests a larger adult. But paw size varies a lot and some breeds simply have big or small feet for their size. Use it as one clue alongside the parents’ size, the breed, and the growth-rate estimate from the calculator above.
How can I tell how big a mixed-breed puppy will get?
With no papers, lean on three things: the calculator’s growth-rate estimate, the size of the parents if you can find out, and a DNA test if you want certainty. Shelters and fosters can often tell you the mother’s size, which is the single best predictor. As a rough rule, a puppy is roughly half its adult weight at around 4 to 5 months for medium breeds.
Does a bigger dog cost more to own?
Yes. Large and giant breeds eat far more food, need larger doses of flea, tick, and heartworm prevention, and cost more for boarding and some procedures. They also tend to have shorter lifespans. If you are weighing a big breed, our dog cost calculator can show you the monthly and yearly difference before you commit.