Pet Growth Calculator

The underlying formula, adult weight equals current weight divided by current age in weeks, multiplied by the age (in weeks) at which that pet's size class typically reaches adulthood, is the same age-based extrapolation used by several real veterinary growth calculators. The one improvement this calculator makes over the simplest versions of that formula: instead of assuming every dog matures at exactly 52 weeks, it uses a maturity age matched to breed size class, since a toy dog and a giant breed dog do not grow on the same timeline, a real pattern documented in the WALTHAM Petcare Science Institute's puppy growth charts, a research-backed reference used by veterinarians to monitor puppy growth.

For example, a 4 kg puppy at 12 weeks old with no known breed size class (assumed Medium, maturing around 52 weeks) predicts to about 17.3 kg as an adult. The same 4 kg puppy at 12 weeks, if entered as a Giant breed instead (maturing closer to 90 weeks), predicts a much larger adult weight, since it has far more growing left to do before its size class typically levels off. Once your pet actually reaches its size class's typical maturity age, this calculator simply reports its current weight as the estimate, since there's no more growth left to extrapolate. If you'd like to see how weight prediction connects to the rest of your pet's life stages, our Dog and Cat Age Calculator converts calendar age to human-equivalent years using a similar breed-aware approach.

A quick mental-math alternative some veterinary sources use, if you would rather not do the division: a small puppy has usually tripled its birth weight by around 8 weeks old, while a medium or large puppy has usually doubled its 16-week weight by adulthood. This calculator's own formula produces a similar result across that same age range, just continuously rather than at one fixed checkpoint.

These typical weight ranges by age and breed size class reflect commonly published veterinary growth data and are meant as a general reference, not a precise prediction for any individual pet. Use the calculator above for a number tailored to your own pet's current weight and age.

Kittens grow on a much narrower track than puppies, since almost all cats, regardless of breed, reach most of their adult weight by around 12 months, which is also a normal weight range for a fully grown adult cat.

This calculator groups dogs into five breed size classes, matching the classification widely used across veterinary and pet-industry sources. Picking the closest class, even for a mixed-breed dog, meaningfully improves the prediction over leaving it on "not sure," since it changes both the assumed maturity age and the classification check on your result. Breed size also affects other needs, like daily food portions, so it's worth getting right beyond just this calculator; see our Pet Calorie Needs Calculator if you want a feeding-side estimate too.

A purebred puppy or kitten inherits a fairly consistent, well-documented adult size from its breed, which is why breed-specific growth charts can be so precise. A mixed-breed pet can inherit size genes from two, or more, very different ancestors, so its eventual adult size has a genuinely wider range of realistic outcomes even with the exact same current age and weight as a purebred pet. If you know roughly which breeds are in the mix, choosing the size class of the larger parent breed as your best guess tends to produce a more realistic estimate than defaulting to Medium, since a small-parent, large-parent mix usually lands closer to the larger side once fully grown.

• Dog and Cat Age Calculator: convert your pet's calendar age to human-equivalent years
• Pet Food Portion Calculator: figure out daily feeding amounts based on weight and life stage
• Vet Medication Dosage Calculator: estimate weight-based medication dosing, always confirm with your vet