How we calculate this

PuppySize estimates a puppy's adult weight from one well-established veterinary idea: dogs of a similar adult size follow a similar growth curve, the percentage of their final weight they've reached at each age. If you know how far along that curve a puppy is today, you can project where it will finish. No black box, no proprietary "AI."

The method, in three steps

Find the curve. Every breed maps to one of five size classes: toy, small, medium, large, giant. Each class has a curve of % of adult weight by age, which we computed from about 89,000 healthy dogs aged 2–24 months in the open Salt et al. 2017 dataset.
Project from today. We divide your puppy's current weight by the percentage it has reached at its current age. A 18 lb puppy that's 50% grown projects to roughly a 36 lb adult.
Return a range. The band comes from the same data: the spread between real puppies at that age (the 25th–75th percentiles), clamped to the breed's known adult range. Because puppies converge on their adult weight over time, the range narrows as your puppy gets older rather than using a fixed guess.

What it can and can't do

Estimates are typically within 10–20% for purebreds.
Mixed and designer breeds vary more; two littermates can finish at noticeably different sizes.
The earlier the age, the wider the uncertainty. Re-checking around 4–6 months gives a tighter estimate.
Past a breed's maturity age we report "at or near full size" rather than extrapolating beyond 100%.
Giant breeds (over ~100 lb) rest on fewer records and mature later, so treat those estimates as a bit softer.

Our sources

We build authority through transparent method and real citations, never fabricated vet bylines. See the full sources list, which includes:

Salt et al. 2017, PLOS ONE: the peer-reviewed study (a retrospective analysis of over 6 million young dogs) that established the size-class growth-curve method and released the underlying data.
The open dataset (University of Liverpool DataCat, CC BY 4.0): the actual bodyweight-and-age records. We filtered it to ~89,000 healthy dogs aged 2–24 months and computed our own per-size-class percentiles from them.
WALTHAM Petcare Science Institute: the research institute that produced this data. (Its own clinical puppy growth charts are a separate product; we derived our curves directly from the open dataset.)
AKC breed standards for purebred adult weight ranges, and GANA and other registry/vet sources for designer breeds.

PuppySize provides estimates, not veterinary advice. For health concerns about your puppy's growth, talk to your veterinarian.

Contains data from Salt C, et al. (2017), Growth standard charts for monitoring bodyweight in dogs of different sizes, PLoS ONE 12(9): e0182064, and the associated University of Liverpool dataset (doi:10.17638/datacat.liverpool.ac.uk/377), used under CC BY 4.0.

Method questions

Why a range instead of one number?

Growth is variable and no model can be exact, so a single figure would be false precision. A range honestly reflects the uncertainty: typically ±10–20% for purebreds, wider for mixes.

What data are the curves based on?

The open dataset published with Salt et al. 2017 (PLOS ONE): veterinary bodyweight-and-age records from a large US network of primary-care hospitals (Banfield), gathered by the WALTHAM Petcare Science Institute. We filtered it to about 89,000 healthy dogs aged 2–24 months, grouped them into five size classes, and computed the growth percentiles ourselves. The data is open under CC BY 4.0.