The growth-curve method
Puppies don't grow linearly — they sprint early and taper off, and the shape of that curve depends on adult size. A small breed is already 40% grown at 12 weeks, while a giant breed is only 22% grown at the same age. This calculator divides your puppy's current weight by the percentage typical for its age and size class to project the adult weight.
Percentage of adult weight by age
| Age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 8 weeks | 25% | 20% | 16% | 13% |
| 12 weeks | 40% | 33% | 27% | 22% |
| 16 weeks | 55% | 45% | 38% | 32% |
| 6 months | 75% | 66% | 55% | 48% |
| 9 months | 90% | 85% | 75% | 65% |
| 12 months | 100% | 95% | 88% | 80% |
Which size class should I pick?
- Small — adult weight under ~20 lb (Chihuahua, Shih Tzu, Dachshund)
- Medium — 20–50 lb (Beagle, Border Collie, Bulldog)
- Large — 50–90 lb (Labrador, German Shepherd, Golden Retriever)
- Giant — over 90 lb (Great Dane, Mastiff, Bernese Mountain Dog)
For mixed breeds, go by the parents if known — or run two size classes and treat the results as your range. Paw size relative to legs is folklore with a grain of truth, but parent size is a far better predictor.
Frequently asked questions
How can I tell how big my puppy will get?
The most reliable everyday method is growth-curve math: puppies of each size class reach a known percentage of their adult weight at a given age. Divide current weight by that percentage. Paw size and parents' weights are useful sanity checks; DNA breed tests are the most precise option for mixed breeds.
At what age is a puppy half its adult weight?
Small breeds hit 50% around 3.5-4 months, medium breeds around 4-5 months, large breeds around 5-6 months, and giant breeds not until about 6-7 months.
When do puppies stop growing?
Small breeds finish around 10-12 months, medium breeds around 12-15 months, large breeds around 18 months, and giant breeds can keep filling out until 24 months.
How accurate is a puppy weight prediction?
Treat it as an estimate with roughly ±15% margin. Genetics, litter variation, nutrition and neuter timing all influence final size. Predictions get sharper after 16 weeks of age.