PawsMathHow the puppy weight estimate works
Puppies follow a predictable S-shaped growth curve: very fast gains in the first months, then a gradual slow-down until they reach adult weight. What changes between breeds is the timing. A toy breed can be fully grown before its first birthday, while a giant breed keeps growing for up to two years.
The calculator looks up what percentage of adult weight a typical puppy of your size group has reached at your puppy’s age, then divides the current weight by that percentage. For example, a medium-breed puppy at 16 weeks is usually about 42% of its adult weight, so a 17 lb puppy should end up around 40 lb.
Typical % of adult weight by age
| Age | Toy | Small | Medium | Large | Giant |
|---|---|---|---|---|---|
| 8 weeks | 25% | 22% | 18% | 14% | 11% |
| 12 weeks | 40% | 36% | 30% | 24% | 19% |
| 16 weeks | 55% | 50% | 42% | 34% | 28% |
| 24 weeks (6 mo) | 77% | 72% | 63% | 53% | 44% |
| 36 weeks (9 mo) | 93% | 90% | 83% | 74% | 64% |
| 52 weeks (12 mo) | 100% | 99% | 96% | 91% | 84% |
| 78 weeks (18 mo) | 100% | 100% | 100% | 100% | 98% |
These are averages compiled from published growth curves; individual puppies vary.
Healthy growth tips
- Feed a food made for growth, and for large and giant breeds, a "large-breed puppy" formula with controlled calcium. Too much calcium or calories can harm developing joints.
- Lean is better than chubby. Puppies that grow slowly and stay lean have fewer joint problems later. You should be able to feel the ribs easily.
- Weigh every 1–2 weeks and track the trend. Sudden plateaus or weight loss warrant a vet visit.
- Plan for size. Use the estimate to choose a crate (see our crate size calculator), harness and food. Bigger dogs cost noticeably more to keep; the pet cost calculator gives a yearly estimate by size.
Your questions answered
How accurate is a puppy weight calculator?
Expect an estimate within about 15% for most healthy puppies. Genetics, diet, neutering age and mixed parentage all change the final size. Predictions get more accurate the older the puppy is when you measure.
At what age is a puppy half its adult weight?
Small breeds hit about half their adult weight around 11–12 weeks, medium breeds around 15–16 weeks, large breeds around 20–22 weeks and giant breeds closer to 26–28 weeks.
When do dogs stop growing?
Small breeds usually reach adult weight at 9–12 months, medium breeds at 12–15 months, large breeds at 15–18 months and giant breeds at 18–24 months.
Do paw size and parents’ weight predict adult size?
Parents’ weights are the single best predictor. Most puppies end up close to the same-sex parent. Big paws are a rough hint at best and are not reliable on their own.
Which size category should I choose for a mixed breed?
Choose based on the expected adult weight of the parents or the dominant breed. If unsure, try two categories. The true answer is usually between them, and the estimate will narrow as your puppy grows.
Sources
A calculator can't examine your dog. If anything seems off, or you're unsure, your veterinarian is the right person to ask. Disclaimer