How the estimate works
Puppies follow an S-shaped growth curve: slow at first, fastest in the middle, then leveling off. A 2004 study in the Journal of Nutrition (Hawthorne et al.) weighed 173 puppies of 12 breeds every week and fitted each breed to a logistic growth curve. The calculator uses the published curve for the breed you pick to work out what share of adult weight your puppy has reached, then divides:
Estimated adult weight = weight now ÷ share
x₀ is the age in weeks when puppies of that breed reach half their adult weight, and b sets how fast they grow (1/b is the weekly growth rate the study reports).
Worked example
A 12-week-old Labrador puppy weighs 20 lb. For Labradors, x₀ = 18.6 weeks and 1/b = 13.7% per week, so b = 7.30. Share = 1 ÷ (1 + e−(12 − 18.6)/7.30) = 1 ÷ (1 + e0.904) = 1 ÷ 3.47 = 28.8%. Adult weight ≈ 20 ÷ 0.288 = about 69 lb.
The breeds in the study
| Breed | Average adult weight | Weeks to half-grown (x₀) | Weeks to 99% grown |
|---|---|---|---|
| Papillon (toy) | 2.2 kg (5 lb) | 11.1 | 41.7 |
| Cairn Terrier (small) | 6.3 kg (14 lb) | 15.5 | 42.9 |
| Miniature Schnauzer (small) | 7 kg (15 lb) | 14.1 | 41.3 |
| Cocker Spaniel (small) | 10.2 kg (22 lb) | 16.6 | 46.6 |
| English Springer Spaniel (medium) | 14.8 kg (33 lb) | 14.3 | 39.4 |
| Beagle (medium) | 17.4 kg (38 lb) | 14.8 | 41.9 |
| Labrador Retriever (large) | 28.1 kg (62 lb) | 18.6 | 52.1 |
| Newfoundland (giant) | 43.3 kg (95 lb) | 18.5 | 46.1 |
| Great Dane (giant) | 51.1 kg (113 lb) | 18.1 | 52.1 |
| Irish Wolfhound (giant) | 52.4 kg (116 lb) | 19.1 | 49.1 |
| St. Bernard (giant) | 65.2 kg (144 lb) | 21.9 | 56.7 |
| English Mastiff (giant) | 66.9 kg (147 lb) | 22.9 | 65.2 |
When do puppies stop growing?
Small breeds finish first. The AKC says small breeds usually stop growing by 6 to 8 months, medium breeds around 12 months, and giant breeds keep growing until 12 to 18 months, with some very large breeds such as Mastiffs taking about 2 years. In the study above, toy and small breeds reached 99% of adult weight by about 41–47 weeks, Labradors by 52 weeks and Mastiffs by 65 weeks.
Limits: this is an estimate
- Each breed's curve is an average of a few to a few dozen puppies; individual dogs vary, and males are usually bigger than females.
- Mixed-breed puppies may not follow any one breed's curve. Pick the breed closest to the size you expect.
- The study weighed puppies from 8 weeks (some from birth), so the calculator works from 8 weeks. Very young puppies' estimates swing a lot with small weight changes.
- A puppy that's underweight or overweight now will throw off the estimate. Ask your vet about body condition, and don't change your puppy's food to hit a target weight without their advice.
Sources
- Hawthorne AJ, Booles D, Nugent PA, Gettinby G, Wilkinson J. Body-Weight Changes during Growth in Puppies of Different Breeds. J Nutr. 2004;134(8):2027S–2030S growth curves (Table 1).
- AKC: When Does My Puppy Finish Growing?
- Salt C, et al. Growth standard charts for monitoring bodyweight in dogs of different sizes. PLoS One. 2017;12(9):e0182064 growth standard charts by size.