What will my puppy’s weight be?
Enter your puppy's weight, age and breed size. The calculator estimates the adult weight and draws how the weight should grow from here.
- Estimated adult weight
- 43.8 lb
A Medium (10 to 25 kg / 22 to 55 lb) puppy weighing 20 lb at 16 wk should grow to about 43.8 lb.
- Grown so far
- 46%
Estimated adult weight: 43.8 lb. A Medium (10 to 25 kg / 22 to 55 lb) puppy weighing 20 lb at 16 wk should grow to about 43.8 lb.
Expected weight by age
How to calculate
Estimates a puppy’s adult weight from its current weight, age and size class with a logistic growth curve from a study of puppy growth, and draws the expected growth by age.
Example with the default inputs (Current weight 20 lb, Age 16 wk, Size of breed Medium (10 to 25 kg / 22 to 55 lb)): A Medium (10 to 25 kg / 22 to 55 lb) puppy weighing 20 lb at 16 wk should grow to about 43.8 lb.
Formula: adult weight = current weight ÷ f, where f = 1 ÷ (1 + exp(−(age in weeks − x0) ÷ b)) and b = (T99 − x0) ÷ ln 99, with x0 and T99 set per size class (Hawthorne et al. 2004).
- Growth follows a logistic curve, the form Hawthorne et al. (2004) fitted to puppies of 12 breeds. Real puppies vary a lot around any curve.
- x0 (weeks to half of adult weight) and T99 (weeks to 99%) per size class: toy 11.1 and 39, small 14.05 and 41, medium 17 and 43.5, large 19.95 and 52, giant 22.9 and 65. The toy and giant x0 are the Papillon and English Mastiff values from the study; the other x0 are equal steps between them, and each T99 is inside the ranges the study reports (about 9 to 10 months for toy to medium breeds, 11 to 15 months for large and giant breeds).
- The age is from 8 weeks to 2 years, and weights are at most 150 kg (331 lb). Mixed breeds: pick the size you expect the adult to be.
Worked examples
Each example is checked against the calculator on every build.
- Size of breed Medium (10 to 25 kg / 22 to 55 lb), Current weight 20 lb, Age 16 wk gives Estimated adult weight 43.8 lb, Grown so far 45.675811%.Source: hand calculation in content.mdx: b = (43.5 − 17) ÷ ln 99 = 5.767; f = 1 ÷ (1 + e^((17 − 16) ÷ 5.767)) = 0.45676; 9.0718 kg ÷ 0.45676 = 19.86 kg (43.8 lb) (Hawthorne et al. 2004 logistic form)
- Size of breed Toy (adult under 5 kg / 11 lb), Current weight 2.425 lb, Age 11.1 wk gives Estimated adult weight 4.9 lb, Grown so far 50%.Source: Hawthorne et al. (2004): Papillons reach 50% of their 2.2 kg adult weight at 11.1 weeks; at t = x0 the logistic fraction is exactly 1/2, so 1.1 kg ÷ 0.5 = 2.2 kg
- Size of breed Giant (over 45 kg / 100 lb), Estimated adult weight 147.5 lb, Age 22.9 wk gives Current weight 73.74 lb.Source: Hawthorne et al. (2004): English Mastiffs (66.9 kg adult) reach 50% at 22.9 weeks; 66.9 × 0.5 = 33.45 kg
- Size of breed Large (25 to 45 kg / 55 to 100 lb), Current weight 66.14 lb, Estimated adult weight 66.8 lb gives Age 52 wk.Source: definition of T99 in content.mdx: at 99% of adult weight the curve gives the class T99, 52 weeks for large breeds
How it works
Hawthorne and others (2004) weighed puppies of 12 breeds as they grew and fitted a logistic (S-shaped) curve to each breed. The calculator uses the same form, with one curve per breed size:
- f = 1 ÷ (1 + exp(−(t − x0) ÷ b))
- adult weight = current weight ÷ f
Here t is the age in weeks, f is the share of adult weight reached at that age, x0 is the age in weeks at which a puppy reaches half its adult weight, and b sets how fast the curve rises. b comes from T99, the age at which the puppy reaches 99% of adult weight: T99 = x0 + b × ln 99, so b = (T99 − x0) ÷ ln 99.
| Size (typical adult weight) | x0 (weeks) | T99 (weeks) | b (weeks) |
|---|---|---|---|
| Toy (under 5 kg / 11 lb) | 11.1 | 39 | 6.072 |
| Small (5 to 10 kg) | 14.05 | 41 | 5.865 |
| Medium (10 to 25 kg) | 17 | 43.5 | 5.767 |
| Large (25 to 45 kg) | 19.95 | 52 | 6.975 |
| Giant (over 45 kg / 100 lb) | 22.9 | 65 | 9.162 |
Where the numbers come from: the toy and giant x0 values are the Papillon (11.1 weeks) and English Mastiff (22.9 weeks) values in the study. The small, medium and large x0 values are equal steps between those two. Each T99 is inside the ranges the study reports: about 9 to 10 months for toy to medium breeds and 11 to 15 months for large and giant breeds.
The same equation, rearranged, gives the current weight from an adult weight (current = adult × f), or the age at which the puppy reaches its current share of adult weight (t = x0 − b × ln(adult ÷ current − 1)).
The calculator also shows grown so far = current weight ÷ adult weight × 100%. The chart draws the curve for the estimated adult weight, in kilograms, from 8 to 78 weeks, with a marker at your puppy's age.
Assumptions
- Growth follows the logistic curve for the chosen size. Individual puppies can be well above or below it.
- The age is from 8 weeks to 2 years. Weights are at most 150 kg (331 lb).
- The current weight must be below the adult weight when you solve for the age.
Worked examples by hand
A medium puppy of 20 lb at 16 weeks. b = (43.5 − 17) ÷ ln 99 = 26.5 ÷ 4.5951 = 5.767. f = 1 ÷ (1 + exp((17 − 16) ÷ 5.767)) = 1 ÷ (1 + 1.1893) = 0.45676. 20 lb = 9.0718 kg. Adult weight = 9.0718 ÷ 0.45676 = 19.86 kg (43.8 lb). Grown so far: 45.7%.
A toy puppy of 1.1 kg at 11.1 weeks. At t = x0 the exponent is 0, so f = 1 ÷ (1 + 1) = 0.5. Adult weight = 1.1 ÷ 0.5 = 2.2 kg, the adult weight of the Papillons in the study.
A giant puppy that will weigh 66.9 kg, at 22.9 weeks. Again t = x0, so f = 0.5. Current weight = 66.9 × 0.5 = 33.45 kg.
When a large-breed dog reaches 99% of adult weight. t = x0 − b × ln(1 ÷ 0.99 − 1) = 19.95 + b × ln 99 = 19.95 + 32.05 = 52 weeks, the class T99.
Other questions people ask
How can I predict my puppy's adult weight?
Divide the current weight by the share of adult weight a puppy of that size and age usually has. A medium-breed puppy at 16 weeks is at about 46% of its adult weight on this curve, so 20 lb now suggests about 20 ÷ 0.457 = 44 lb as an adult.
When do puppies stop growing?
In a study of 12 breeds (Hawthorne and others, 2004), toy, small and medium breeds reached 99% of their adult weight at about 9 to 10 months. Large and giant breeds took about 11 to 15 months.
How accurate is a puppy weight estimate?
It is a rough guide. Puppies of the same breed differ, and food, neutering and health all change growth. The estimate is less certain for young puppies and for mixed breeds. Your vet can compare your puppy with growth charts over several visits.
Why does breed size matter?
Small breeds grow fast and finish early; giant breeds keep growing for months longer. In the same study, Papillons reached half their adult weight at 11.1 weeks, and English Mastiffs at 22.9 weeks.
What if my puppy is a mixed breed?
Pick the size class you expect the adult dog to be in, for example from the parents' weights. If you are unsure, try the two nearest classes to see a range.
Is the doubling at 16 weeks rule right?
Rules such as "double the weight at 16 weeks" are rough. On these curves, a medium-breed puppy at 16 weeks is at about 46% of its adult weight, which is close to doubling, but a toy puppy is well past half, and a giant puppy is well short of it.