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.
Dog aging by breed — 30 popular breeds
Size class drives the math, and breed tells you the size class. Find your breed below (or the closest match by adult weight) to see its typical lifespan, when it's considered senior, and what age 7 looks like in human years.
| Breed | Size class | Typical lifespan | Senior from (yrs) | Age 7 in human yrs |
|---|---|---|---|---|
| Chihuahua | Small | 14–16 yrs | 10 | ~44 |
| Yorkshire Terrier | Small | 11–15 yrs | 10 | ~44 |
| Pomeranian | Small | 12–16 yrs | 10 | ~44 |
| Shih Tzu | Small | 10–16 yrs | 10 | ~44 |
| Dachshund | Small | 12–16 yrs | 10 | ~44 |
| Maltese | Small | 12–15 yrs | 10 | ~44 |
| Toy Poodle | Small | 14–18 yrs | 10 | ~44 |
| Boston Terrier | Small | 11–13 yrs | 10 | ~44 |
| Beagle | Medium | 10–15 yrs | 9 | ~47 |
| French Bulldog | Medium | 10–12 yrs | 9 | ~47 |
| Cocker Spaniel | Medium | 10–14 yrs | 9 | ~47 |
| Border Collie | Medium | 12–15 yrs | 9 | ~47 |
| Bulldog | Medium | 8–10 yrs | 9 | ~47 |
| Pembroke Welsh Corgi | Medium | 12–13 yrs | 9 | ~47 |
| English Springer Spaniel | Medium | 12–14 yrs | 9 | ~47 |
| Whippet | Medium | 12–15 yrs | 9 | ~47 |
| Labrador Retriever | Large | 11–13 yrs | 8 | ~50 |
| Golden Retriever | Large | 10–12 yrs | 8 | ~50 |
| German Shepherd | Large | 9–13 yrs | 8 | ~50 |
| Boxer | Large | 10–12 yrs | 8 | ~50 |
| Standard Poodle | Large | 12–15 yrs | 8 | ~50 |
| Doberman Pinscher | Large | 10–12 yrs | 8 | ~50 |
| Siberian Husky | Large | 12–14 yrs | 8 | ~50 |
| Vizsla | Large | 12–14 yrs | 8 | ~50 |
| Rottweiler | Giant | 9–10 yrs | 6–7 | ~58 |
| Great Dane | Giant | 7–10 yrs | 6–7 | ~58 |
| Saint Bernard | Giant | 8–10 yrs | 6–7 | ~58 |
| Bernese Mountain Dog | Giant | 7–10 yrs | 6–7 | ~58 |
| Newfoundland | Giant | 9–10 yrs | 6–7 | ~58 |
| Great Pyrenees | Giant | 10–12 yrs | 6–7 | ~58 |
What actually determines adult size
Genetics sets the ceiling; nutrition decides whether a puppy reaches it on schedule. Parent size is the strongest predictor available at home — for mixed breeds, average the parents and lean toward the mother. What doesn't work: overfeeding to "grow them bigger" (it grows them fatter, and in large breeds it accelerates growth in ways that harm developing joints), and paw-size folklore (paws correlate loosely at best). If the projection above matters for a real decision — apartment rules, crate purchase, insurance tier — a DNA breed test tightens the estimate more than any formula can.
Using the projection well
Weigh every two weeks and compare against the curve, not against other puppies: steady progress along any track matters more than the track itself. A projection that keeps drifting upward usually means the size class is wrong — re-run with the next class up and see which curve your weigh-ins actually follow. For large and giant breeds, the practical takeaways from a big projection are worth acting on early: large-breed puppy food (controlled calcium), no forced running before growth plates close (~12–18 months), and an adult-size crate with a divider instead of two crate purchases.
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.