# What will my puppy’s weight be?

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.

- Page: https://www.acalculator.org/biology/puppy-weight-calculator
- JSON spec: https://www.acalculator.org/biology/puppy-weight-calculator.json
- Version: fbdf50e8177a

## Default answer

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.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| w | Current weight | The puppy’s weight today. |
| age | Age | The puppy’s age today, from 8 weeks to 2 years. |
| adult | Estimated adult weight | The weight the growth curve predicts once the dog is fully grown. |
| size | Size of breed | The size class of the breed, by typical adult weight. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| current | Current weight | The puppy’s weight today. |
| age | Age | The puppy’s age today, from 8 weeks to 2 years. |
| adult | Estimated adult weight | The weight the growth curve predicts once the dog is fully grown. |
| grown | Grown so far | The current weight as a share of the estimated adult weight. |

## Method

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).

## Assumptions

- 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

1. size = medium, w = 9.071847, age = 9,676,800 gives adult = 19.861382, grown = 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).
2. size = toy, w = 1.1, age = 6,713,280 gives adult = 2.2, grown = 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.
3. size = giant, adult = 66.9, age = 13,849,920 gives w = 33.45. Source: Hawthorne et al. (2004): English Mastiffs (66.9 kg adult) reach 50% at 22.9 weeks; 66.9 × 0.5 = 33.45 kg.
4. size = large, w = 30, adult = 30.30303 gives age = 31,449,600. Source: definition of T99 in content.mdx: at 99% of adult weight the curve gives the class T99, 52 weeks for large breeds.

## FAQ

### 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.

## Sources

- Hawthorne, A. J., D. Booles, P. A. Nugent, J. Wilkinson, and G. Gettinby (2004). Body-weight changes during growth in puppies of different breeds. Journal of Nutrition 134(8), 2027S–2030S. https://doi.org/10.1093/jn/134.8.2027S
- Salt, C., P. J. Morris, A. J. German, D. Wilson, E. M. Lund, T. J. Cole, and R. F. Butterwick (2017). Growth standard charts for monitoring bodyweight in dogs of different sizes. PLoS ONE 12(9), e0182064. https://doi.org/10.1371/journal.pone.0182064
- NIST Special Publication 811 (2008), Appendix B.8: 1 lb = 0.45359237 kg exactly. https://www.nist.gov/pml/special-publication-811