Why we built this
Pet questions rarely come with a number attached — "how old is she really?", "how much should I feed him?", "what size crate?". CritterCalc answers them with clear, source-backed math for dogs, cats, and fish, so you get a trustworthy starting point in seconds instead of conflicting forum threads.
How we calculate
Every tool uses an established formula. The table documents the exact math and key assumptions behind each calculator.
| Calculator | Core formula | Key assumptions |
|---|---|---|
| Dog Age | Yr 1 = 15, yr 2 = +9, then +4–6/yr by size | Bigger dogs age faster (not ×7). |
| Cat Age | Yr 1 = 15, yr 2 = 24, then +4/yr | AAHA/AVMA life stages. |
| Puppy Weight | Adult ≈ (current ÷ age in weeks) × 52 | Best between 8–20 weeks; breed varies. |
| Dog Food | RER = 70 × kg^0.75; MER = RER × factor; cups = MER ÷ kcal/cup | AAFCO/NRC; vet-reviewed. |
| Dog Calories | RER = 70 × kg^0.75; MER = RER × factor | AAFCO/NRC; vet-reviewed. |
| Cat Food | RER = 70 × kg^0.75; MER = RER × factor | AAFCO/NRC; vet-reviewed. |
| Dog Pregnancy | Due = breeding date + 63 days (58–68) | Gestation varies slightly. |
| Crate Size | Length + 4 in, height + 4 in → standard size | Puppies: buy adult size + divider. |
| Water Intake | ≈ 1 oz per lb per day (½–1 oz/lb) | More when hot/active. |
| Fish Tank Volume | Gallons = L × W × H ÷ 231 | 231 cu in/gal (exact); ~10% less stocked. |
| Litter Box | Boxes = cats + 1 | Standard feline-welfare rule. |
| Walk & Exercise | Daily minutes = breed baseline × age factor | Energy level + life stage. |
The calculators run entirely in your browser in plain JavaScript. Nothing you type is sent to a server or stored — your pet's details stay on your device.
Accuracy, sources & veterinary review
Formulas and constants come from recognized references: the American Kennel Club and modern dog-aging research (age), AAHA/AVMA life-stage guidance (cat age), and AAFCO/NRC/WSAVA veterinary-nutrition standards (the RER/MER feeding and calorie tools). **Our feeding and calorie calculators are reviewed by a licensed veterinarian**, and each tool carries its own cited source and a review date.
Methodology last reviewed June 2026 · Feeding tools veterinarian-reviewed
What this is not
CritterCalc gives helpful estimates to guide everyday pet care. It is not veterinary advice and never replaces your vet — especially for feeding a puppy, pregnant, or unwell animal, for medication, or for any health concern. When in doubt, call your veterinarian.
Get in touch
Want a calculator we don't have yet, or spot a number that looks off? Tell us on the contact page.