How to use the puppy weight calculator
- Weigh your puppy (a bathroom scale works: weigh yourself holding the puppy, then subtract your own weight).
- Enter its age in weeks.
- Choose the size you expect as an adult. For a mixed breed, pick the size of the bigger parent if you are not sure.
- Read the estimated adult weight, the share of adult weight it has reached, and when it should be fully grown.
The formula
Puppies follow an S-shaped growth curve that flattens as they near adult size, and larger breeds take longer. WALTHAM’s puppy growth charts, built from data on about 50,000 dogs, note that small dogs (under 9 kg) are full grown at about 12 months, 30–40 kg dogs at about 18 months and giant breeds at almost two years.
We turned that into a simple curve. The share of adult weight at age t months is:
share = (1 − e^(−k × t))², with k = 5.3 ÷ months to adult size
The 5.3 makes the curve reach 99% of adult weight at the full-grown age: 10 months (toy), 12 (small), 15 (medium, our interpolation), 18 (large) and 24 (giant).
Adult weight ≈ weight now ÷ share
This is our own model fitted to those ages, not a published chart, so use the answer as a rough guide.
Tips
- Re-check monthly. Estimates get better as your puppy gets older.
- Grow big puppies slowly. Large and giant breed puppies should not be pushed to grow fast. Feed a large-breed puppy food and use the puppy food calculator.
- Plan the crate. Buy a crate for the adult size with a divider. The dog crate size calculator helps.
Sources
- WALTHAM Petcare Science Institute: puppy growth charts (waltham.com).
- Salt C. et al. (2017). Growth standard charts for monitoring bodyweight in dogs of different sizes. PLOS ONE 12(9): e0182064.
- Hawthorne A.J. et al. (2004). Body-weight changes during growth in puppies of different breeds. Journal of Nutrition 134: 2027S–2030S.
Frequently asked questions
How big will my puppy get?
A puppy’s adult size depends mostly on its breed or mix and its parents. This calculator gives an estimate from how much of its adult weight a puppy of that size has usually reached at its age. For a pedigree puppy, the parents’ weights and the breed standard are often the best guide.
How much will my puppy weigh as an adult?
Divide its weight now by the share of adult weight a puppy of its size and age has usually reached; the calculator does this for you. For a pedigree, the breed standard and the parents’ weights are often a better guide. Treat any answer for a young puppy as a rough guide and re-check monthly.
How much weight should a puppy gain per week?
There is no single number: toy puppies may gain a few ounces a week and giant breeds several pounds. What matters is a steady curve and a good body shape (ribs easy to feel, a visible waist). Weigh every week or two and ask your vet if growth stalls or shoots up.
At what age is a puppy half its adult weight?
It depends on size: small breeds get there much sooner than large and giant breeds. WALTHAM notes that small dogs (under 9 kg) are full grown in about a year, a 30–40 kg dog in about 18 months, and some giant breeds take almost two years.
Can paw size predict how big a puppy will get?
Not reliably. Big paws are a fun clue, but paw size varies between breeds and between puppies in the same litter. Weight at a known age, the breed and the parents’ size are better guides.