Puppy Weight Calculator
Enter your puppy’s weight, age in weeks, and expected breed size to estimate adult weight. The classic breeder rules of thumb — like doubling the 4-month weight for medium breeds — are built in.
Example: with Current weight (lb) 12 · Age (weeks) 14 · Expected breed size Medium (20–50 lb adult) → Estimated adult weight: 30.0 lb.
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outHow big will my puppy get?
The estimate divides current weight by age in weeks, then multiplies by a growth constant for the breed-size class — the math behind the classic breeder rules. For small breeds it reproduces “adult weight ≈ 4 × the 6-week weight” (or 3 × the 8-week weight): a 4-lb, 8-week-old Cavalier projects to about 12 lb. For medium breeds it matches “double the weight at 4 months”: a 12-lb puppy at 14 weeks projects to 30 lb. For large and giant breeds it’s “double the weight at 6 months”: a 33-lb, 26-week-old shepherd mix projects to about 66 lb.
Treat the number as a planning figure, not a promise — the parents’ adult sizes are still the best predictor, and nutrition, sex, and spay/neuter timing all nudge the outcome. Estimates made before 8 weeks or for mixed breeds carry the most uncertainty.
How it’s calculated
Estimated adult weight = current weight (lb) ÷ age (weeks) × K, where K is 24 for toy/small, 35 for medium, and 52 for large/giant breeds. These constants encode the widely used breeder rules of thumb: small breeds ≈ 4× their 6-week weight, medium breeds ≈ 2× their 4-month (≈17.5-week) weight, and large/giant breeds ≈ 2× their 26-week weight (equivalently, weight ÷ weeks × 52). Past K weeks the entered weight is shown as adult weight. Kilograms use 1 lb = 0.4536 kg.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Weighing at under 6 weeks and extrapolating — early weights reflect the litter more than the dog, so wait for the 8-week vet visit.
- Picking the size class from the puppy’s current look instead of the parents’ adult weights.
- Reading the estimate as exact: real adult weights commonly land 10–20% either side, especially for mixed breeds.
Frequently asked questions
How can I tell how big my puppy will get?
Divide its weight by its age in weeks and multiply by 24 (small), 35 (medium), or 52 (large/giant breeds). Checking the parents’ adult weights is the best reality check on the result.
How much will my puppy weigh at maturity if it's 10 lb at 8 weeks?
A small breed projects to about 30 lb — which really means it isn’t small: at 10 lb and 8 weeks, use the medium constant, giving roughly 44 lb.
At what age is a dog full grown?
Small breeds finish around 10–12 months, medium breeds 12–15 months, and large or giant breeds keep growing until 18–24 months (AKC guidance).
Do big paws mean a big dog?
Only loosely — paw size is a folk indicator with plenty of exceptions. Age-for-weight math and the parents’ sizes predict far better.
How accurate are puppy weight calculators?
They’re estimates: purebreds with known parents often land within about 10%, while mixed breeds can miss by 20% or more in either direction.