Free puppy weight calculator — predict your puppy's adult size using the veterinary formula. Enter current weight and age in weeks for an instant adult weight estimate.
The standard veterinary formula for estimating a puppy's adult weight is: Adult Weight = (Current Weight in lbs ÷ Age in Weeks) × 52. This works because most dogs reach their adult weight within roughly 52 weeks (one year) for small and medium breeds.
The formula is most accurate when used between 12 and 20 weeks of age. Very young puppies (under 12 weeks) are still in a phase of highly variable growth that makes prediction less reliable. Giant breeds that take 18-24 months to fully mature will require adjustment.
For mixed-breed dogs with unknown parentage, the breed size category gives you a working estimate. If you can see both parents, averaging their weights gives a more reliable prediction than the formula alone.
This formula gives estimates within 10-15% for most dogs at 12-20 weeks. Giant breeds and mixed breeds have higher variability. Genetics, nutrition quality, and individual variation all affect final adult size. Use as a planning guide, not a guarantee.
Percentage of adult weight typically reached at each age milestone, by breed size category.
| Age | 🐩 Small (<20 lb) | 🐕 Medium (20-50 lb) | 🪶 Large (50-90 lb) | 🐻 Giant (90+ lb) |
|---|---|---|---|---|
| 8 weeks | ~10% adult wt | ~10% adult wt | ~12% adult wt | ~8% adult wt |
| 12 weeks | ~30% adult wt | ~30% adult wt | ~30% adult wt | ~25% adult wt |
| 16 weeks | ~50% adult wt | ~45% adult wt | ~40% adult wt | ~35% adult wt |
| 6 months | ~75% adult wt | ~65% adult wt | ~55% adult wt | ~45% adult wt |
| 9 months | ~95% adult wt | ~85% adult wt | ~75% adult wt | ~65% adult wt |
| 12 months | ~100% adult wt | ~100% adult wt | ~90% adult wt | ~80% adult wt |
| 18 months | 100% adult wt | 100% adult wt | ~100% adult wt | ~95% adult wt |