Puppy Weight Calculator: Estimate Adult Size from Age

Puppies of every size grow fast at first and then level off, but big breeds keep growing for months longer. If you know what share of its adult weight a puppy usually has at a given age, you can work backward from today’s weight to a rough adult size. This calculator does that with the growth curves of 12 breeds published by Hawthorne and colleagues in The Journal of Nutrition (2004).

Where the curves come from

The study weighed 173 puppies of 12 breeds, from the 2.2 kg Papillon to the 66.9 kg English Mastiff, every week until about 12 months (toy to medium breeds) or 18 months (large and giant breeds). All lived at the same research center and ate complete growth diets. For each breed the authors fitted a logistic growth curve to the average weights and published its three parameters:

weight at age x = a ÷ (1 + e^{−(x − x0) / b})

• a is the breed’s average adult weight,
• x0 is the age in weeks at which the puppies reached half of it,
• 1/b is the early growth rate, in % per week (so b = 100 ÷ rate).

Dividing both sides by a gives the share of adult weight at any age. The calculator computes that share for your puppy’s age on the curve you pick and divides today’s weight by it:

Estimated adult weight = weight today ÷ share of adult weight at this age

Share of adult weight by age

Breed curve	Adult weight	8 wk	12 wk	16 wk	20 wk	26 wk	39 wk	52 wk
Papillon	5 lb	39%	53%	68%	79%	90%	99%	99%+
Cairn Terrier	14 lb	22%	36%	52%	68%	86%	98%	99%+
Miniature Schnauzer	15 lb	26%	41%	58%	73%	88%	99%	99%+
Cocker Spaniel	22 lb	21%	33%	48%	63%	81%	97%	99%+
English Springer Spaniel	33 lb	24%	40%	58%	74%	89%	99%	99%+
Beagle	38 lb	24%	38%	55%	71%	87%	98%	99%+
Labrador Retriever	62 lb	19%	29%	41%	55%	73%	94%	99%
Newfoundland	95 lb	15%	25%	40%	56%	78%	97%	99%+
Great Dane	113 lb	20%	31%	43%	56%	74%	94%	99%
Irish Wolfhound	116 lb	15%	25%	38%	53%	74%	95%	99%+
St. Bernard	144 lb	14%	21%	31%	44%	63%	91%	98%
English Mastiff	147 lb	16%	23%	32%	42%	58%	85%	96%

Calculated from the published curve parameters (Hawthorne et al. 2004, Table 1). Adult weight is the study’s mean, converted from kg. 26 weeks ≈ 6 months, 52 weeks ≈ 12 months.

Small breeds are already at about half their adult weight by 12–16 weeks; the English Mastiff reaches half its adult weight at about 23 weeks. The study found that toy, small and medium breeds reached 99% of adult weight at about 9–10 months, and large and giant breeds at about 11–15 months.

Worked examples

Example 1: a 16-week-old Labrador Retriever puppy weighing 20 lb. On the Labrador curve, a 16-week-old puppy has 41% of its adult weight. 20 ÷ 0.412 = 48.6 lb estimated adult weight. The Labradors in the study averaged 28.1 kg (62 lb) as adults, so this puppy is on the small side of that group, or is simply growing at its own pace.

Example 2: a 12-week-old Beagle weighing 8 lb. Share at 12 weeks on the Beagle curve: 38%. 8 ÷ 0.383 = 20.9 lb.

Example 3: a 26-week-old (6-month-old) Great Dane weighing 70 lb. Share at 26 weeks: 74%. 70 ÷ 0.744 = 94.1 lb. Giant breeds still have a quarter of their growth ahead at six months.

Limitations

• Twelve breeds, small groups. Some curves rest on very few dogs (3 Papillons, 4 English Mastiffs, 4 St. Bernards). Breeds of similar size can still grow differently: the authors’ analysis separated Labrador Retrievers from Beagles and Springer Spaniels, and Newfoundlands from the other giant breeds.
• Averages, not targets. The curves describe average weights of puppies in one colony. They are not the “right” weight for your puppy. Faster growth isn’t better: the study’s authors point out that overfeeding large-breed puppies causes musculoskeletal disorders as well as obesity.
• Sex matters. The authors note that males and females may grow differently, and their curves mix both.
• Young puppies. At 8–12 weeks a puppy has only a small share of its adult weight, so small differences in today’s weight make big differences in the estimate. Weigh again every few weeks and watch the estimate settle.
• Mixed breeds. No curve was fitted for mixed-breed dogs. Picking the curve of a similar-sized breed is our suggestion, not something the study tested.

For how much to feed while your puppy grows, see the puppy feeding calculator.