Puppy feeding and growth
Is there a formula to estimate a puppy's adult size?
Last updated 23 September 2026 · How we write and check this
Short answer
A commonly used rough formula for medium and large breeds is doubling a puppy's weight at 14 weeks, though it is only an approximation and works less well for very small or giant breeds. Growth calculators that factor in breed and current age generally give a more reliable estimate.
The doubling rule and its limits
For many medium and large breed puppies, weight at around 14 weeks roughly doubles by adulthood, which gives a quick ballpark figure. It tends to underestimate toy and small breeds, which grow proportionally faster early on, and can be inaccurate for giant breeds, whose growth curve stretches out much longer.
A percentage based alternative
Another approach uses the rough percentage of adult weight typical for a breed's size category at a given age, for example a large breed puppy being around 60 percent of adult weight at six months, then working backward from current weight to estimate the eventual total.
Why breed specific tools do better
Because growth curves differ so much between size categories, a calculator that accounts for breed or expected adult size category tends to be noticeably more accurate than a single formula applied to every puppy, especially outside the medium to large breed range the doubling rule was built around.
Key takeaways
- Doubling a puppy's weight at 14 weeks is a rough estimate mainly suited to medium and large breeds.
- The formula tends to be less accurate for toy, small, and giant breeds.
- Percentage of adult weight by age is an alternative way to estimate final size.
- A breed aware growth calculator generally beats a single formula applied to all dogs.