About the Puppy Weight Calculator
This puppy weight calculator predicts your puppy’s adult weight from three things you already know: its current weight, its age in weeks and its expected size class. It shows the estimated adult weight in pounds and kilograms, how much of its final size the puppy has already reached, and a projected growth curve up to two years old.
It is useful when you have adopted a mixed-breed puppy and want to know how big it will get, when choosing a crate, harness or bed that will still fit later, or when checking that a puppy is growing at a healthy pace. Small breeds finish growing by around 9–10 months, while giant breeds can keep filling out until 18–24 months.
The estimate divides current weight by the typical fraction of adult weight reached at that age for the chosen size class. Those fractions are our own rule-of-thumb curves, not figures from a single published dataset. They are shaped to match published research that larger breeds grow for longer: very small dogs reach adult weight at about 8–12 months and larger breeds need up to 24 months (Salt et al., PLOS ONE 2017; Hawthorne et al., J Nutr 2004). They are not breed-specific, so individual puppies, especially mixes, can finish 10–20% above or below the prediction. Predictions made after 16 weeks are usually more reliable than very early ones.
With the default inputs, the estimated adult weight is 34.9 lb. Change any value above to recalculate instantly.
How to use the puppy weight calculator
- 1Weigh your puppy and enter the weight in pounds or kilograms.
- 2Enter its age in weeks (months × 4.3).
- 3Pick the expected adult size class — use the parents’ size or breed if you know it.
- 4Read the predicted adult weight and check the growth curve.
- 5Re-weigh every few weeks and update the estimate.
Formula and method
F is the typical fraction of adult body weight a puppy of the chosen size class has reached at its current age. The calculator stores F at 12 checkpoints between 8 and 104 weeks for each size class and interpolates linearly between them. For example, a medium puppy is around 43% of its adult weight at 16 weeks, so 15 lb ÷ 0.43 ≈ 35 lb.
The F values are rule-of-thumb estimates, not taken from one published growth study. They follow the pattern reported in veterinary growth research: smaller breeds grow fast and finish early (about 9–10 months here), while large and giant breeds grow for longer (15–24 months). Because they are averages for a size class, treat the result as a likely range of about ±15% rather than an exact figure. If you know the parents’ weights, those are usually a better guide.
- F
- Fraction of adult weight typically reached at this age for this size
- Current weight
- Puppy’s weight today (lb or kg)
Worked examples
16-week medium puppy weighing 15 lb
Medium puppies are typically about 43% of adult weight at 16 weeks. 15 ÷ 0.43 = 34.9 lb, so expect an adult around 35 lb (roughly 30–40 lb).
12-week large-breed puppy at 20 lb
A large-breed puppy is usually about 26% grown at 12 weeks, so 20 ÷ 0.26 ≈ 77 lb — typical of a Labrador- or shepherd-sized adult.
5-month (22-week) small puppy at 3 kg
At 22 weeks a small breed is halfway between the 20-week (64%) and 24-week (75%) checkpoints, about 69.5%. 3 kg ÷ 0.695 ≈ 4.3 kg (about 9.5 lb) as an adult, so about 1.3 kg still to gain.
Frequently asked questions
How can I tell how big my puppy will get?+
The best clues are the parents’ weights, the breed or likely breed mix, and the puppy’s current weight for its age. Growth-curve calculators like this one turn current weight and age into an adult estimate; paws and skin looseness are much less reliable.
At what age is a puppy half its adult weight?+
Small breeds are about half-grown around 14–15 weeks, medium breeds around 18–19 weeks, large breeds around 22–23 weeks and giant breeds around 28 weeks, based on typical growth curves.
When do dogs stop growing?+
Toy and small breeds usually finish growing at 9–10 months, medium breeds at about 12 months, large breeds at 15–18 months and giant breeds at 18–24 months, though they may keep adding muscle afterwards.
How accurate is a puppy weight calculator?+
Expect roughly ±15%. Mixed breeds, the wrong size class, illness or over- and under-feeding all affect the result. Estimates from 16 weeks onwards are more reliable than from 8 weeks.
Is my puppy overweight?+
Weight alone cannot tell you. Vets use body condition scoring: you should be able to feel the ribs easily under a thin fat layer and see a waist from above. Ask your vet if you are unsure.