Dog Size Calculator (predict your puppy’s adult weight)

Understanding the puppy adult size calculator — concept and principle

This calculator predicts a puppy's adult weight from its breed, age in weeks and current weight, using breed growth curves published by Posada and colleagues. Owners use it to choose a crate, a bed or a harness, and to check that growth is roughly on track.

Growth curve to adult weight: with the default inputs the result is 31.3 kg adult (≈ 69 lb · 21.8 kg at 6 months).

How it is calculated

Share of adult weight at age t (weeks) = 1 ÷ (1 + e^−(t − x₀)/b)

Predicted adult weight = current weight ÷ share

x₀ is the age at which a puppy of the breed reaches half its adult weight; b sets how fast growth runs. Both come from the study.
Weight in 4 weeks = adult weight × share at t + 4; weight at 6 months = adult weight × share at 26 weeks.
The study also gives the age at 99% of adult weight and the breed's average adult weight.

The principle

Puppies grow along an S-shaped (logistic) curve: slowly at first, then very fast, then levelling off as they approach adult size. If you know where on its breed's curve a puppy is, you know what fraction of its final weight it has reached, and dividing the current weight by that fraction scales it up to an adult prediction. Small breeds finish growing at about 9–12 months, large breeds at 12–16 months. Because the curve is steep early on, predictions made on very young puppies are the least certain.

Worked example

Default inputs: Labrador Retriever, 16 weeks, 11 kg. Labrador parameters: x₀ = 20.26 weeks, b = 6.96.

Share at 16 weeks = 1 ÷ (1 + e^((20.26 − 16) ÷ 6.96)) = 1 ÷ (1 + 1.844) = 0.352, shown as 35%.
Adult weight = 11 ÷ 0.3516 = 31.3 kg = 69 lb.
At 20 weeks the share is 0.491, so weight in 4 weeks = 31.28 × 0.491 = 15.4 kg.
At 26 weeks the share is 0.695, so weight at 6 months = 21.8 kg.
Labradors reach 99% at 52 weeks; study average adult weight 29.5 kg; stage fast growth phase.

Each point is the calculator re-run with only “Current weight (kg)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Current weight (kg)	Predicted adult weight (kg)
2.75	7.8
5.5	15.6
8.25	23.5
11	31.3
13.8	39.1
16.5	46.9
22	62.6

How to read the result

A prediction close to the breed average suggests typical growth. A much higher figure may mean the puppy is from larger lines, or carrying extra fat. Use the 4-week forecast as a check: weigh again then and see whether the puppy is close. For mixed breeds, choose the breed nearest in size and treat the result as rough.

Common mistakes

Using the tool on puppies under 8 weeks.
Picking a breed of very different size for a mixed-breed puppy.
Comparing weights taken at different times of day or after a meal.
Feeding to reach a predicted weight faster; fast growth harms large-breed joints.

Keep in mind: The study used small groups of dogs and individual puppies differ. This is an estimate, not a diagnosis; ask your vet if growth seems too fast or too slow.

Frequently asked questions

How big will my Labrador puppy get?

Divide its weight by the share of adult weight for its age; at 16 weeks a Labrador is about 35% grown.

When do dogs stop growing?

Small breeds at about 9–12 months, large breeds at about 12–16 months.

Is paw size a good predictor?

It is a common folk guide, but the weight-curve method is based on measured growth data.

Sources: Posada S., Gómez L., Rosero R. (2014), "Application of the logistic model to describe the growth curve in dogs of different breeds", Revista MVZ Córdoba 19(1):4015–4022

Checked 9 Nov 2026. Posada S., Gómez L., Rosero R. (2014), “Application of the logistic model to describe the growth curve in dogs of different breeds”, Revista MVZ Córdoba 19(1):4015–4022, Table 2 (adult weight a, b, x₀ and time to 99% of adult weight per breed).

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