Dog Size Calculator — Predict Adult Weight from Puppy Age
Enter your puppy's current age in weeks, weight, and breed-size category to estimate the adult weight your dog will likely reach — with the projected growth curve plotted week by week.
Breed size category
weeks
Weight unit
kg
Rough estimate ±20–30 % — actual weight varies with genetics and nutrition
- 1
Growth fraction
(8 ÷ 57)^0.75 = 0.2293Power-law model — fraction of adult size reached at the current age. - 2
Predicted adult weight (kg)
2.5 ÷ 0.2293 = 10.9
How does this calculator work?
Predicted adult weight ≈ current weight ÷ (age / maturity_age)^0.75, where maturity_age depends on breed size (36–104 weeks). Useful within ±20–30 %; compare with parent weights for a better bound. The growth curve flattens sharply after ~50 % of adult age.
Formula
How this is calculated
Dogs do not grow at a constant rate: they gain weight quickly in the first few months, then taper off as they approach their adult size. A power-law model with an exponent of 0.75 approximates this decelerating growth — the same family of relationships (Kleiber's law) that connects body mass to metabolic rate across animals. Dividing the puppy's current weight by the estimated growth fraction gives the predicted adult weight.
The expected maturity age depends on breed size: toy breeds are fully grown by about 9 months (36 weeks); small breeds by 11 months; medium breeds by 13 months; large breeds by 18 months; and giant breeds such as Great Danes by 24 months. The growth fraction at any age is (age / maturity)^0.75, capped at 1 once the dog passes its maturity milestone.
This is a rough estimate with typical uncertainty of ±20–30 %. Genetics (parentage), sex (males are usually heavier), diet, and health all shift the final weight significantly. Mixed breeds are harder to predict. For the most accurate forecast, compare against measured weights at 8 and 16 weeks and consult your vet.
Frequently asked questions
The model typically comes within ±20–30 % of the actual adult weight for purebred dogs of known size class. Accuracy is lower for mixed breeds and for predictions made very early (under 6 weeks) or near maturity when error accumulates.
If your dog is at or past the expected maturity age for its size class, the calculator returns the current weight as the adult weight, since growth is essentially complete.
Yes — male dogs are typically 15–20 % heavier than females of the same breed. The calculator does not split by sex; apply a rough correction if needed.
TG we-Calculate Editorial Team. (2026). Dog Size Calculator — Predict Adult Weight from Puppy Age [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/dog-size-calculator
TG we-Calculate Editorial Team. "Dog Size Calculator — Predict Adult Weight from Puppy Age." TG we-Calculate. 2026. https://we-calculate.com/calculator/dog-size-calculator.
TG we-Calculate Editorial Team, "Dog Size Calculator — Predict Adult Weight from Puppy Age," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/dog-size-calculator
@misc{wecalculate_dog_size_calculator, title = {Dog Size Calculator — Predict Adult Weight from Puppy Age}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/dog-size-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?