How we calculate
Last updated: October 10, 2026
Every number on PawScales comes from a named source. Below is each constant, its value, and the source we took it from with the date we checked it. The puppy growth table has its own method, described at the end.
| Constant | Value | Source |
|---|---|---|
| Dog gestation from first breeding | 63 days ±7 | Cornell Riney Canine Health Center, Normal whelping process |
| Dog gestation from ovulation | 63 days ±2 | Cornell Riney Canine Health Center |
| Pre-labor temperature drop | below 99°F (normal 100–102.5°F) | Cornell Riney Canine Health Center |
| X-ray to count puppies | after day 55 | Merck Veterinary Manual (owner) |
| Whelping box ready | at least 5 days before the due date | American Kennel Club, whelping and caring for newborn puppies |
| Heat interval (interestrous) | 7 months (4–13) | Merck Veterinary Manual (owner) |
| Proestrus / estrus length | about 9 days each | Merck Veterinary Manual (owner) |
| Resting energy requirement | RER = 70 × kg^0.75 | Pet Nutrition Alliance, Calculating Calories |
| Dog MER: neutered / intact adult | 1.6 / 1.8 × RER | Pet Nutrition Alliance |
| Dog MER: growth (<4mo / ≥4mo) | 3 / 2 × RER | Pet Nutrition Alliance |
| Cat MER: neutered / intact adult | 1.2 / 1.4 × RER | Pet Nutrition Alliance |
| Treats budget | 10% of daily calories | WSAVA / AAHA guidance |
| Individual variation | up to 50% | Pet Nutrition Alliance |
| Dog age (DNA formula) | 16 * ln(age) + 31 | Wang T, et al. Cell Systems 2020;11(2):176-185. DOI 10.1016/j.cels.2020.06.006 |
| Dog age (size chart) | AVMA size-based chart, ages 1–16 | https://www.avma.org/resources-tools/pet-owners/petcare/selecting-pet-dog |
| Cat age after 2 years | +4 human years per cat year | International Cat Care |
Puppy growth table
The puppy weight calculator uses growth data on 60,951 dogs (199,355 vet visits) from Salt et al. (2017), via the open Liverpool Data Catalogue (CC BY 4.0). We keep dogs that were a healthy weight as adults, group them into five adult-size bands, measure what share of their 2-year weight they reached at each age, smooth the curve, and normalize it so 100% is the 2-year weight. Full detail is on the puppy weight calculator.