Methodology and Sources
Last updated: November 1, 2026
Every calculator on PawNumbers is built around a published formula or a standard veterinary guideline. This page explains the families of formulas we use, the organisations we reference, and the limits that apply to all of them.
Formula families
- Feeding: resting energy requirement (70 × body weight in kg0.75), multiplied by a life-stage factor, then converted to cups using the food’s kcal per cup. This is the approach used in veterinary nutrition guidance.
- Water: 50-60 ml/kg baseline for dogs and 45-60 ml/kg for cats, adjusted for diet, heat and activity. These are ranges, not precise prescriptions.
- Age: 15 human years for the first year, 24 at the second, then size-based ageing for dogs and four years per year for cats.
- Chocolate toxicity: average theobromine content by chocolate type, converted to mg per kg of body weight and compared with published risk thresholds.
- Crate sizing: body length and shoulder height plus 2-4 inches, rounded up to standard crate sizes, with a weight minimum.
- Pregnancy: 63 days for dogs (normal 58-68) and 64 days for cats (normal 61-72) from the breeding date.
- Costs: typical U.S. ranges from industry spending surveys, presented as ranges rather than quotes.
Reference organisations
We draw on guidance from the following organisations. Links go to their main sites so you can read the current guidance yourself; we are not affiliated with them.
- Merck Veterinary Manual — clinical reference for toxicosis, reproduction and nutrition.
- WSAVA — global nutrition and life-stage guidance.
- AVMA — dog age conversion guidance and animal health resources.
- AAHA — life-stage and preventive care guidelines.
- American Association of Feline Practitioners — feline life-stage and senior care guidance.
- ASPCA Animal Poison Control — chocolate and household toxin information.
- Cornell Feline Health Center — feline hydration and urinary health.
- American Pet Products Association — pet spending data used for cost ranges.
- American Kennel Club — breed size and crate guidance.
What no calculator can do
These formulas assume a healthy animal of average body condition. They cannot account for medical conditions, medications, pregnancy complications, breed-specific risks or laboratory results. A number from this site is a starting point for a conversation with a veterinarian, not a diagnosis or a treatment plan.
Corrections
If you find an error, email hello@pawnumbers.com with the page URL and the source you are comparing against. Corrections are reviewed and applied to the calculator and the written explanation together.