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Calculator Answers

Puppy Weight Calculator

Blake Boege
Written by Blake Boege · Founder, Calculator Answers

A puppy weight calculator is a veterinary science utility that estimates the adult weight of a young dog based on its current weight, age, and breed size. It uses growth curve formulas for small, medium, large, and giant breeds, predicting how much additional weight a puppy will gain before reaching skeletal maturity. The calculator also provides a projection of the growth timeline, showing when the dog is expected to stop growing. Pet owners and veterinarians use this tool to monitor growth progress and manage nutritional requirements.

Enter your puppy's current age, weight, and breed-size bracket. The calculator back-solves an adult weight range from the growth curve this page publishes below.

See also: Dog Age Calculator, Dog Food Calculator, and Pet Weight Converter.

Quick Answer

Estimate the full-grown weight of your puppy. Enter your puppy's current weight, age in weeks, and breed size to predict their adult weight.

Current age

Weeks is more precise for very young puppies. 1 month ≈ 4.3 weeks.

lb

Expected adult breed size

Small (under 20 lb)

Estimated adult weight

Range estimate (±15%)

8.5–11.5 lb

Center estimate: 10 lb

Center estimate10 lb
Low end8.5 lb
High end11.5 lb
Currently45% of adult
Age (weeks)12
BracketSmall (under 20 lb)

Growth varies by breed, parent size, neutering, nutrition, and genetics. Treat this as a planning estimate, not a forecast.

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Examples

Small · 12 weeks · 4.5 lb

≈ 8.5–11.5 lb adult

Medium · 16 weeks · 18 lb

≈ 28–38 lb adult

Large · 20 weeks · 32 lb

≈ 45–61 lb adult

Giant · 24 weeks · 50 lb

≈ 71–96 lb adult

How it works

At any age, a puppy weighs some fraction of the weight it will reach as an adult. The calculator looks up that fraction for your bracket and age, then divides to back-solve:

Estimate · adult weight = current weight ÷ (fraction of adult at this age)

The plus or minus 15 percent range is this page's stated convention for showing uncertainty, not a measured error bar. The curve itself is this page's own, and the section below sets it beside the one published curve so you can see where they part.

Where this curve comes from

It is this page's own table. Not a publication, not a veterinary standard, and not the study most calculators point at. Saying so costs nothing and is the only honest description.

Looking for a source to use instead turned up three things worth passing on. No veterinary body publishes a percentage-of-adult-weight table at all. The 2019 and 2021 American Animal Hospital Association guidelines contain no such figures, and defer to the growth charts below.

The famous puppy growth charts do not publish percentages. Salt and colleagues in PLOS ONE (2017), and the WALTHAM charts built on that work, plot absolute kilograms against age as population centiles for dogs up to 40 kg from 12 weeks. A centile there is the proportion of dogs below the line, which is a different quantity entirely. Several calculators credit that paper for percentage tables it does not contain, and this page will not join them.

One published curve does exist, and it is compared against this one in the next section rather than quietly borrowed from.

This curve against the published one

FEDIAF's Nutritional Guidelines (Table VII-8a, September 2025) publish growth equations of the form % of mature weight = a × ln(age in weeks) − b, bracketed by expected adult weight and valid from weaning at 8 weeks to 1 year. Setting the two side by side:

Bracket8 wk12 wk16 wk24 wk36 wk
Small, this page25%45%65%90%100%
FEDIAF ≤7 kg33.2%48.2%58.8%73.8%88.7%
Medium, this page22%38%55%80%93%
FEDIAF >15–27.5 kg22.2%38.4%49.9%66.0%82.2%
Large, this page18%33%50%70%85%
FEDIAF >27.5–47.5 kg20.7%35.7%46.3%61.3%76.3%
Giant, this page15%25%38%60%—
FEDIAF >47.5 kg13.7%28.6%39.1%54.0%68.8%

They agree closely at 8 and 12 weeks, then this page runs high through the middle of the curve: 16.2 points high for a small dog at 24 weeks, 14.0 for a medium one. A curve that reads high in the middle produces an adult estimate that reads low, because the current weight is divided by it. At 24 weeks in the small bracket, this page divides by 0.90 where FEDIAF would divide by 0.738, which is about 22 percent less adult weight.

The comparison stops at the edges of what FEDIAF covers. This page's 4-week row, and everything past 52 weeks, has no published counterpart to be checked against at all.

Working one out by hand

Take a small-bracket puppy of 4.5 lb at 12 weeks.

  1. Read the fraction for the bracket and age. Small at 12 weeks is 0.45.
  2. Divide. 4.5 ÷ 0.45 = 10 lb central estimate.
  3. Apply the stated range. 10 × 0.85 = 8.5 and 10 × 1.15 = 11.5, so 8.5 to 11.5 lb.
  4. Between the table's anchor ages the fraction is interpolated in a straight line. At 14 weeks, halfway between the 12-week 45 percent and the 16-week 65 percent, it uses 55 percent.

The doubling rules, and where they disagree with this page

You will meet these everywhere. None of them carries an attribution, and this page's own curve implies different multipliers:

The ruleSaysThis curve implies
Small, weight at 6 weeks× 4× 5.71
Medium, weight at 6 weeks× 4× 6.67
Small, weight at 14 weeks× 2× 1.82
Medium, weight at 14 weeks× 2× 2.15
Large, weight at 6 months× 2× 1.38
Giant, weight at 6 months× 2× 1.62

The six-week rule is the worst of them, understating a medium puppy's adult weight by around 40 percent. The six-month doubling rule fails in the other direction: a large-breed puppy of 40 lb at six months comes out at 80 lb by the rule and 55 lb by this curve. These are not small disagreements, and this page publishes them rather than quietly picking one.

Edge cases

  • Very young puppies. Below the first anchor the curve runs in a straight line back to zero, which is a modelling convenience rather than a claim about newborns. Estimates here divide by a very small number and swing wildly on small errors.
  • Past the ceiling. Once the curve reaches 100 percent the estimate simply returns the current weight. A small-bracket dog at 40 weeks is treated as fully grown, which is this page's assumption and is earlier than the published equation would have it.
  • Months against weeks. A month here is 4.345 weeks, the average calendar month, not four. Over six months that is a difference of about two weeks, which matters most at the steep part of the curve.
  • The wrong bracket. The single largest source of error, and the one the range does not cover. Small and giant differ by more than 30 points of adult fraction at 24 weeks, so a misjudged bracket moves the answer far more than the stated 15 percent.

What this page will not tell you

It projects a weight. It does not assess whether your puppy is growing correctly, does not recommend a feeding amount, and does not say whether a difference from littermates matters. Those require examining the animal, and the arithmetic here cannot substitute for it at any level of confidence.

Related: Dog age calculator for converting years, dog food calculator for portion arithmetic, and pet weight converter for units.

Your figures stay in this page

The age, weight and bracket you enter are computed by this page in your browser. Nothing is sent to a server, nothing is stored after you close the tab, and there is no account.

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Dog Age CalculatorConvert your dog's age to human years using the modern logarithmic formula, with breed-size adjustments.Dog Food CalculatorEstimate how much food your dog needs each day, based on weight, life stage, activity, and the calories per cup of your food.Pet Weight ConverterConvert pet weights between pounds, ounces, kilograms, and grams — useful for food labels, vet records, and weight tracking.

Frequently asked questions

The calculator looks up what fraction of its adult weight a puppy in your size bracket has typically reached at your puppy's age, then divides the current weight by that fraction to back-solve for adult weight. A puppy at 45 percent of its adult weight weighing 4.5 lb gives 4.5 divided by 0.45, which is 10 lb. The output is shown as a range because a single figure would overstate what this can know.

This page's own table, and that is worth saying plainly because most pages will not. The figures are not taken from a publication. They are a hand-drawn curve through plausible values, which is why they land on round numbers like exactly 90 and exactly 100 rather than on the ragged decimals a fitted curve produces. Below there is a comparison against the one published percentage-of-adult-weight curve found, so you can see exactly where this page differs from it.

One, and it is cited on this page: FEDIAF's Nutritional Guidelines give logarithmic growth equations by expected mature bodyweight, valid from weaning at 8 weeks to 1 year. It was not adopted here because it stops at 1 year and starts at 8 weeks, and this calculator accepts ages outside both ends. Where the two overlap they are compared row by row below rather than quietly averaged.

They say something different, and this matters because many calculators cite them for tables they do not contain. Salt and colleagues (PLOS ONE, 2017) and the WALTHAM charts built from that work plot absolute bodyweight in kilograms against age as population centiles. A centile there is the share of dogs below that line, not a share of adult weight. Neither publishes a percentage-of-adult-weight figure at any age, and both cover 12 weeks to 2 years for dogs up to 40 kg only.

Because the people who tried to build one concluded it could not be done. The WALTHAM guide states that growth patterns among giant breeds differ so markedly that a single chart cannot represent dogs above 40 kg, and that validated charts for that size are not available. This page does offer a giant bracket. Treat it as the roughest of the four, for that reason.

It is folklore in the strict sense: it appears on dozens of sites and none of them attributes it to anyone. It is also inconsistent with this page's own curve, and the section below shows by how much. Any rule that ignores breed size has to be wrong at one end or the other, because a toy and a mastiff are at very different fractions of their adult weight on the same birthday.

Less accurate than the tidy range implies. The range shown is plus or minus 15 percent around the central estimate, which is a stated convention of this page rather than a measured error bar: nobody has tested this curve against a population and reported its spread. Genetics, parent size, breed mix, nutrition and neutering timing all move the answer, and a mixed-breed puppy of unknown parentage is the hardest case of all.

Nobody, as far as this page could establish. There is no standard definition of small, medium, large and giant by adult weight from any kennel club or veterinary body. Published work uses its own internal cut-offs and they disagree with each other: the WALTHAM categories break at 6.5, 9, 15, 30 and 40 kg, while FEDIAF breaks at 7, 15, 27.5 and 47.5 kg. Pick the bracket that matches the adult weight you expect rather than a label.

Because the inputs do not determine the output. Two puppies of the same age, weight and bracket can finish several pounds apart on genetics alone. A calculator that returns one exact figure is not more accurate than one that returns a range; it is the same guess with the uncertainty hidden.

Smaller dogs finish earlier than larger ones, and the growth in height finishes before the filling out does. This page's curve reaches its ceiling at 36 weeks for the small bracket and 104 weeks for the giant one, which is the curve's own assumption rather than a published finding. The published FEDIAF equations do not settle it either: they stop at one year, and for a small dog the equation is still climbing past 100 percent at that point.

It means the litter has a spread, which litters do. Size within a litter varies and the largest puppy at eight weeks is not reliably the largest adult. What this page can tell you is what its curve implies for the weight you typed; what it cannot tell you is whether the difference matters, which is a question for someone who can examine the animal.

You can, with the accuracy caveat doing real work. The calculator needs a size bracket, and for a mix of unknown parentage that bracket is itself a guess. If you are wrong about the bracket you will be wrong about the answer by more than the plus or minus 15 percent range suggests, because the brackets differ from each other by more than 15 percent at most ages.

Because early in the curve you are dividing by a small number. At four weeks the small bracket is at 10 percent, so the estimate is the current weight times ten, and a quarter-pound of scale error becomes two and a half pounds of adult weight. The same error at 24 weeks, where you divide by 0.9, moves the answer by barely a quarter pound. Estimates made very early are arithmetically fragile.

No, and it is not the right tool to ask. This page divides one number by another to project a weight. Feeding amounts depend on the food, the individual and the growth stage, and getting them wrong in either direction has consequences that a projection cannot see. That is a conversation to have with a vet.

No. The age, weight and bracket are computed by this page in your browser. Nothing is sent to a server, nothing is kept after you close the tab, and there is no account.