Quick answer: Adult weight = current weight ÷ growth completion for your puppy’s age and size. A medium puppy weighing 10 lb at 16 weeks is about 50% grown, so it should reach about 20 lb. Toy and small breeds finish by around 12 months; large and giant breeds keep filling out until 18 to 24 months.
How the calculator predicts adult weight
adult weight = current weight ÷ growth completionGrowth completion = fraction of adult weight reached for age and sizePuppies grow fastest early and slow near maturity, so the percentage-of-adult-weight method is more accurate than a straight line. The percentages follow published canine growth curves, including American Kennel Club guidance.
A medium puppy at 10 lb and 16 weeks
- Growth completion at 16 weeks: about 50%
- Adult weight: 10 ÷ 0.50 = 20 lb
Result: about 20 lb
The linear shortcut, (weight ÷ weeks) × 52, gives 32.5 lb for the same puppy. It over-predicts because it assumes growth never slows.
Puppy growth chart: percentage of adult weight
| Age | Toy | Small | Medium | Large | Giant |
|---|---|---|---|---|---|
| 8 weeks | 30% | 27% | 22% | 18% | 14% |
| 12 weeks | 45% | 42% | 36% | 30% | 24% |
| 16 weeks | 60% | 55% | 50% | 43% | 35% |
| 6 months | 80% | 75% | 65% | 55% | 45% |
| 9 months | 93% | 90% | 83% | 75% | 65% |
| 12 months | 100% | 98% | 95% | 88% | 78% |
| 18 months | 100% | 100% | 100% | 97% | 92% |
The calculator interpolates between these rows. Individual dogs can sit 10 to 15% above or below the curve.
Which adult size should I choose?
| Size class | Adult weight | Example breeds |
|---|---|---|
| Toy | Under 12 lb | Chihuahua, Pomeranian, Yorkshire Terrier |
| Small | 12 – 25 lb | Beagle, Mini Schnauzer, French Bulldog |
| Medium | 25 – 50 lb | Border Collie, Cocker Spaniel, Bulldog |
| Large | 50 – 100 lb | Labrador, Golden Retriever, German Shepherd |
| Giant | Over 100 lb | Great Dane, Mastiff, Saint Bernard |
For mixed breeds, follow the larger parent breed and treat the result as a range.
Why predict your puppy's adult weight?
- Buy gear once: crate, bed, harness and car restraint.
- Plan feeding: portions are based on expected adult weight.
- Plan space and budget for a bigger dog.
- Track healthy growth against the curve.
Tips for a more accurate estimate
- Weigh at the same time of day, before a meal.
- Use weeks, not months, under six months old.
- Re-check every few weeks.
- Confirm the size class with your vet or a breed DNA test.
Please note: This is an estimate, not veterinary advice. Do not change feeding based on the result; ask your vet about growth and healthy weight.
Frequently asked questions
How accurate is a puppy weight calculator?
Usually within 10 to 15% for a purebred of known size, and more accurate as the puppy ages. Genetics, sex and nutrition all shift the final figure.
How do I calculate my puppy’s adult weight?
Divide current weight by the fraction of adult weight reached for its age and size. A medium puppy at 10 lb and 16 weeks is about 50% grown, so 10 ÷ 0.50 = 20 lb.
Is this based on the AKC method?
The size classes and growth percentages follow standard canine growth curves, including American Kennel Club guidance.
At what age is a puppy half its adult weight?
About 3 to 3.5 months for toy and small breeds, 4 months for medium, 5 months for large and around 7 months for giant breeds.
When do puppies stop growing?
Toy breeds by about 12 months, medium by 12 to 15, large by 15 to 18 and giant breeds as late as 18 to 24 months.
Can I use this for a mixed-breed puppy?
Yes. Choose the size class of the larger parent breed and treat the answer as a range.
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Accuracy note: Growth percentages are checked against published canine growth curves, including AKC guidance. Results are estimates for planning only; speak to your vet about feeding and growth.
Content Lead, Anchor AI Tools, California, USA. Spotted an error? Email hello@anchoraitools.com and it will be checked and corrected. See our editorial standards.