Puppy Weight Calculator: Predict Your Dog’s Adult Weight

How the puppy weight calculator works

The puppy weight calculator divides your puppy’s current weight by the share of adult weight that dogs of its size class have usually reached at its age. A 4-month-old large-breed puppy at 20 lb is at about 51% of adult weight on the median curve, so the calculator returns roughly 39 lb, and a range either side of it.

The shares come from Salt, Morris, Wilson, Lund and German (2017), Growth standard charts for monitoring bodyweight in dogs of different sizes, PLoS ONE 12(9), and the open dataset published with it: 8,459,668 bodyweight records from Banfield Pet Hospital clinics in the United States, 1994–2013, kept where the visit was for preventive care and the dog was not recorded as thin or heavy. For every size class, sex and month of age, the calculator holds the 25th, 50th and 75th percentile of that share. The 50th gives the single figure; the 25th and 75th give the range. How the percentiles were derived, and what they cannot tell you, is set out on the growth data page.

Choosing a breed does one extra thing: the range is then capped at that breed’s adult weight under the American Kennel Club standard, split by sex. The growth curve is the same, because the source study found that dogs of similar adult size grow on similar curves whatever the breed. For the weight in pounds and kilograms that each share implies at each month, use the puppy growth chart by age.

How accurate is a puppy weight calculator?

A puppy weight calculator built on growth percentiles is exactly as accurate as the spread between those percentiles at the age you enter, and this one can state that spread. At 2 months the range it returns runs from about 20% below the single figure to about 30% above it for every size class: a puppy at that age can sit anywhere in a wide band and still be normal. By 6 months the band has narrowed to about −12% to +15% for large and giant breeds, −13% to +17% for medium and −15% to +19% for small, and it changes little after that.

Toy breeds are the exception. Their band stays at roughly −24% to +30% from 2 months to 12 months and does not narrow with age, because by 24 months the spread between the percentiles is the spread of adult size, and adult toy dogs vary more, relative to their size, than adult large dogs do. A 4-month-old toy puppy’s estimate is therefore no tighter than a 2-month-old’s; what improves it is knowing the breed.

Three limits of the underlying data apply to every estimate here. The records are of dogs attending veterinary clinics, not a random sample of all dogs. Body condition was not recorded on 93% of the rows, so only dogs explicitly noted as thin or heavy could be excluded, and some overweight dogs will remain in the curves. And the source study could not fit models to dogs over 40 kg, so the giant-class percentiles are our own calculation from the same records, and the medium class is interpolated between its neighbours. All three are explained on the growth data page rather than hidden.

What changes the estimate

Age. An estimate made at 8 weeks is the widest the calculator will ever give, because most of the growth is still to come and a small measurement error is multiplied by a large factor. Every size class passes the halfway point at a different age: about 3 months for a toy breed, 4 for small and medium, 4 to 5 for large and 5 for giant, as the table above shows. Enter a later weight and the range tightens for every class except toy.

Breed, or size class without it. A breed is a narrower version of its size class: the same curve, capped at that breed’s adult standard. If you do not know the breed, or the dog is a mixed breed, leave the field blank and the calculator infers a size class from the age and weight you enter. The size class charts show what each class looks like month by month, and the breed weight charts give the breed-specific version.

Sex. Male and female curves separate early and in most breeds the gap is wide enough to matter by 6 months. Selecting a sex switches the calculator to that curve; the breed pages print both.

When growth ends. Large breeds reach 95% of adult weight at about 13 months, toy breeds not until 14 to 17. The calculator applies the 18-month share to any dog older than that. The ages at which each class finishes, and why weight settles later than height, are on when do dogs stop growing.

When to weigh again

Weigh a puppy weekly to about four months, fortnightly to six, then monthly, and write the figure down each time. The trend across several weighings is what carries information; a single reading can move a small dog by several percent depending on a meal or a full bladder, and weighing daily mostly records what the puppy last ate.

The calculator does not store your entries, so the record is yours to keep, but the line it describes is the thing to watch: a puppy holding a steady position in its range is on track whatever the absolute number, and a puppy that has dropped from one part of the range to a lower one is worth a vet visit. Once the line goes flat, the question changes from growth to condition, and the body condition score is the way to answer it.

Frequently asked questions