How the puppy weight calculator works
What the estimate is
Puppies grow along orderly curves, the same way children do. Given an age, a weight, and a sex, the calculator finds the family of growth curves a puppy of that size is traveling among and reads off the adult weight each curve leads to.
The big number is the middle of that family. The range beneath it is the 25th to 75th percentile of the adult weights the curves allow, rounded outward so the range is never narrower than the math supports. In 5 lb steps at or above 40 lb, otherwise 1 lb.
Where the data comes from
The growth standards were fit to the published centile charts of the Waltham Centre’s study of healthy dogs, by Salt and colleagues in PLOS ONE, 2017. That study did for puppies what the World Health Organization’s standards did for children. The fitted parameters, their sources, and the checks they passed are recorded in the open in the site’s repository.
A known breed narrows the range from the start, using adult weight ranges from breed standards, each cited to its source. A mixed breed starts wider. If you know the mother’s weight, it pulls the middle of the range toward her.
What half grown and full grown mean
Half grown is the date the middle curve crosses 50 percent of the predicted adult weight. That date is sharp enough to show with a day.
Full grown is the date the middle curve crosses 95 percent of the predicted adult weight, where growth visibly flattens even though many dogs keep filling out a little after. Because the plateau arrives gradually, that date is honest only to the month, and that is how we show it.
The 88 lb limit
The study behind these charts covers dogs up to about 40 kg, or 88 lb, as adults. When a puppy’s numbers point past that, the calculator says so and keeps the range wide instead of pretending to a precision it does not have. Giant breeds will get a proper chart when a second sourced study is available.
Tracking makes it better
One weigh-in gives a range. Each weigh-in after that refits the whole family of curves, and by the third most puppies have chosen a lane and keep to it. If your puppy leaves the band, the band moves to follow, and the milestone dates move with it. The chart would rather be honest than right.
Saving a puppy keeps everything in your browser on this device. There is no account, and nothing you enter is tied to you.
Caveats
This is an estimate from population growth curves, not a veterinary assessment. Diet, health, and neutering all shift growth. Breed weight ranges come from breed standards and describe typical adults, not every dog. If a puppy is far outside the band, the band will follow, but a vet is the right person to ask why.