Puppy Weight Calculator
How big will your puppy get? Enter their current age and weight and this puppy weight calculator predicts their adult size using the growth-fraction method — the same math breeders and vets use.
Most accurate between 12 and 26 weeks
Mixed breed? Use the parents' average size, or medium if unknown
—
You might also need:Puppy Feeding Calculator·Dog Age Calculator
How the prediction works
(fraction depends on size class — small dogs finish growing much earlier)
An 18 lb medium-breed puppy at 16 weeks has completed roughly 50% of their growth: predicted adult weight ≈ 36 lb. The same weight on a giant-breed schedule (only ~35% grown at 16 weeks) predicts over 50 lb — which is why the size class matters so much.
Percent of adult weight by age
| Age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 8 weeks | 30% | 25% | 20% | 15% |
| 12 weeks | 45% | 38% | 30% | 25% |
| 16 weeks | 60% | 50% | 42% | 35% |
| 6 months | 80% | 70% | 60% | 50% |
| 9 months | 95% | 88% | 80% | 70% |
| 12 months | 100% | 95% | 90% | 80% |
| 18 months | — | 100% | 100% | 95% |
Making the most of the growth months
- Feed for the adult they'll be: large-breed puppies need large-breed puppy food — slower, controlled growth protects joints. Portions in the puppy feeding calculator.
- Buy the crate once: size it for the predicted adult weight with a divider panel — the crate size calculator shows how.
- Track monthly: re-run the prediction as they grow; the estimates converge on the truth by 6 months.
- Curious how old they are in human years? That's the dog age calculator.
Frequently asked questions
How do you predict a puppy’s adult weight?+
The standard method uses growth fractions: at any age, a puppy has completed a known percentage of their growth, which depends on breed size. A medium-breed puppy at 16 weeks is about half grown, so doubling their weight predicts the adult figure. This calculator applies the fraction for your pup’s age and size class.
At what age is a dog full grown?+
Small breeds finish growing around 10–12 months, medium breeds 12–15 months, large breeds 15–18 months, and giant breeds keep filling out until 18–24 months. Growth plates close on that same schedule — why vets advise limiting stairs and big jumps for large-breed puppies.
How accurate are puppy weight calculators?+
For purebreds, expect ±10–20%; parents’ weights are the best sanity check. For mixed breeds accuracy drops — genetics can surprise you. Paw size and loose skin are folk indicators with little predictive value; current weight at a known age is far more reliable.
How can I tell my puppy’s size class if they’re a mix?+
If you know the parents, average their adult weights and pick that class. From a rescue with unknown parents, a DNA test is the reliable answer; otherwise use the calculator with the medium setting at 12–16 weeks and re-check monthly — the trajectory reveals the class quickly.
My puppy is heavier than the prediction — should I worry?+
Puppies grow in spurts, and predictions are averages. A steady body-condition score matters more than the scale: you should feel ribs easily under a thin fat layer. If your pup looks round or you’re unsure, portion sizes are the usual culprit — check the puppy feeding calculator, and ask your vet at the next visit.