Dog and cat ages in human years, diphenhydramine reference doses by weight, daily calorie targets from the RER formula, food portions in cups, and daily water intake — one dropdown for the published pet reference ranges. Every number is a reference to confirm with your veterinarian, not an instruction.
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FORMULA USEDPet Care Calculator
One page of pet math
Pick the pet or the calculation from the dropdown and the form adapts: two fields for an age chart, a unit toggle plus weight for calories and water, the bag's kcal-per-cup for portions. Every result shows the substituted formula beneath the board, so you can read the arithmetic out loud on the phone to your vet.
The formulas that get published
Dog age: year one counts 15 human years, year two adds 9, each later year adds 5 (large breeds age slower on this chart, +4). Cat age: 15, then +10, then +4 a year. Calories: RER = 70 × kg0.75, then × a factor for neuter status and activity — 1.2–1.8 for dogs, 0.8–1.4 for cats. Water: 50–60 ml per kg per day for dogs. Medication reference: diphenhydramine 1 mg/lb (2.2 mg/kg) for dogs, a conservative 0.45 mg/lb (1 mg/kg) for cats.
Worked example
A 3-year-old medium dog: 15 + 9 + 5×1 = 29 human years (large-breed row: 28).
A 25 lb dog against the diphenhydramine reference: 25 lb × 1 mg/lb = 25 mg per dose — then confirm with the vet.
A neutered 20 kg dog: RER = 70 × 20^0.75 ≈ 662 kcal, × 1.4 ≈ 927 kcal per day.
Fed a 350 kcal/cup kibble: 927 ÷ 350 ≈ 2.65 cups per day, split across two meals.
How to use it
Pick the pet or calculation from the dropdown.
Enter the weight in pounds or kilograms — flip the unit toggle first if you need metric.
Read the board; the substituted formula under it shows every step.
Before acting on any dose or diet change, confirm the number with your veterinarian.
Frequently asked questions
How do I calculate my dog’s age in human years?
Use the modern chart, not the 7:1 rule: the first year counts as 15 human years, the second adds 9 (24 total), and every year after adds 5 — so a 3-year-old dog is 29. Large breeds age a bit slower on this scale after year two, +4 per year instead of +5.
Is the “7 dog years per human year” rule real?
It is a myth that overstates young dogs and understates old ones. Dogs hit human-equivalent adulthood by age two (24 human years), then age 4–6 human years per dog year depending on breed size — which is why a Great Dane at 7 is a senior while a Chihuahua at 7 is middle-aged.
How much Benadryl can I give my dog?
The widely published veterinary reference is 1 mg per pound of body weight (2.2 mg/kg), two to three times a day — this page shows that range for your dog’s weight. It is a reference range, not a dosing instruction: confirm the dose and frequency with your veterinarian first, and never give time-release or multi-symptom products containing decongestants or alcohol.
What about diphenhydramine for cats?
Much more caution: cats are sensitive to antihistamines and many vets recommend avoiding them entirely. This page deliberately shows only the conservative 0.45 mg/lb (1 mg/kg) end of the published range. Call your vet before giving a cat anything.
How many calories does my dog or cat need per day?
Start from resting energy, RER = 70 × (weight in kg)^0.75, then multiply by a factor: about 1.4 for a neutered adult dog (1.6 intact, 1.8 active, 1.2 weight loss) and 1.0 for an indoor cat (0.8 weight loss, 1.2–1.4 active). A neutered 20 kg dog lands near 927 kcal/day. Puppies, seniors, and pregnant or lactating pets need their own numbers.
How much food and water is that?
Divide the daily calories by the kcal-per-cup printed on the bag — 927 kcal on a 350 kcal/cup food is about 2.65 cups a day, and keep treats under 10% of calories. For water, dogs need roughly 50–60 ml per kg per day; a 25 kg dog drinks about 1.25–1.5 liters. Sudden changes in either direction are worth a vet call.