Free Pet Calculators for Every Animal Owner
From aquarium gallon volume and chocolate toxicity to dog age conversion and raw feeding ratios: 15 precision tools for US pet owners, completely free and built on verified veterinary and scientific data.
Every calculator uses verified veterinary references, AKC breed standards, and published aquarium science, not guesswork.
Every calculation cites its source, AKC, AAHA, NRC, ASPCA, PNAS, not approximations or myths like “multiply dog years by 7.”
The chocolate toxicity calculator gives clear emergency verdicts. Water weighs 8.34 lbs/gal: our aquarium weight tool tells you if your floor is safe.
All outputs in US gallons, pounds, and Fahrenheit: matching US pet food labels, vet offices, and aquarium store labeling standards.
Works on any phone in a vet waiting room or pet store aisle. No subscription, no account, no ads interrupting your calculation.
15 Pet Tools. All Free. No Signup Required.
Every calculator on this hub is completely free, works on any device, and requires no account. Just enter your numbers and get the answer.
Start with the Toxicity Checker →Pet Feeding, Health, and Aquarium Planning Guide for US Pet Owners
About two thirds of American households share their home with a pet, and the questions they bring to a calculator are surprisingly consistent: how much should my dog eat, how old is my cat really, is the chocolate my dog just ate dangerous, and how heavy will this aquarium be once it is full. The tools in this hub answer those questions with the formulas veterinarians and aquarists actually use, and they always point you back to your vet for anything medical.
Find the right pet calculator
| Question | Calculator | Related |
|---|---|---|
| How many calories does my dog or cat need? | Dog Food Calorie or Cat Food Calorie | Raw Dog Food |
| How old is my pet in human years? | Dog Age or Cat Age | |
| My dog ate chocolate | Dog Chocolate Toxicity | Call your vet |
| When is my pet due? | Dog Pregnancy Due Date or Cat Pregnancy Due Date | |
| Setting up a litter box or small animal cage | Litter Box Size | Guinea Pig Cage Size |
| Planning an aquarium | Aquarium Volume | Aquarium Weight, Heater Size, Chiller Size, Glass Thickness |
The formulas behind the tools
- Resting energy requirement (RER): 70 x (body weight in kg) raised to the 0.75 power. Daily needs are RER times a life-stage factor, for example about 1.6 for a neutered adult dog and about 1.2 for a neutered indoor cat.
- Raw feeding: most adult dogs eat 2 to 3 percent of their ideal body weight per day in raw food, and growing puppies need more.
- Dog age: the first year is roughly 15 human years, the second adds about 9, and each year after adds about 4 to 7 depending on size, with large breeds aging faster.
- Chocolate: the risk comes from theobromine. Mild signs can start around 20 mg per kg of body weight, severe signs around 40 to 50 mg/kg, and seizures around 60 mg/kg. Baking chocolate and cocoa powder carry far more than milk chocolate.
- Pregnancy: dogs and cats both average about 63 days from breeding, with normal variation of a few days either way.
- Aquariums: fresh water weighs about 8.34 pounds per gallon. With glass, substrate, and decor, a set-up tank usually weighs 10 to 12 pounds per gallon. Heaters are commonly sized at 3 to 5 watts per gallon.
- Litter boxes: the box should be about 1.5 times your cat’s length, and most behaviorists suggest one more box than the number of cats.
Three examples
Austin, Texas: 55 pound neutered Lab. 55 pounds is 25 kg. RER = 70 x 25 to the 0.75 power, about 783 calories. Times 1.6 gives about 1,250 calories a day, which is roughly 3.4 cups of a 370 calorie per cup kibble.
Portland, Oregon: 20 pound dog and a 3.5 ounce dark chocolate bar. A 70 percent bar carries roughly 150 to 200 mg of theobromine per ounce, so about 525 to 700 mg in total. The dog weighs 9.1 kg, which works out to roughly 58 to 77 mg/kg, a range where serious signs are likely. This is a call-the-vet-now situation, not a wait-and-see one.
Tampa, Florida: 75 gallon reef tank on a second floor. At 10 to 12 pounds per gallon, the system weighs roughly 750 to 900 pounds, plus the stand. Spread over a footprint of about 4 feet by 1.5 feet, that is well over 100 pounds per square foot, so place it near a load-bearing wall and check with a builder for an older floor.
Common mistakes
- Feeding to the bag chart instead of your pet’s actual activity level and body condition.
- Using the old “multiply by 7” rule for dog age.
- Waiting to see whether symptoms appear after a chocolate or xylitol exposure.
- Filling an aquarium before confirming the stand and floor can carry the weight.
Step by step: setting up a new aquarium
- Calculate volume. Use the Aquarium Volume Calculator with inside dimensions. Real water volume is usually 10 to 15 percent less than the nominal size once substrate and decor go in.
- Check the weight and stand. The Aquarium Weight Calculator tells you what the floor and stand must carry.
- Size the heater and, for warm rooms, a chiller. The heater and chiller calculators work from the gap between room temperature and target water temperature.
- For a custom build, check glass thickness. The glass thickness calculator uses water height, which matters far more than length.
- Cycle the tank before adding fish. Establishing beneficial bacteria typically takes 4 to 6 weeks.
Quick answers
Should I switch my dog’s food all at once? No. Most vets recommend mixing new and old food over 7 to 10 days to avoid stomach upset.
How many litter boxes do I need for two cats? Three is the usual recommendation, placed in different areas of the home.
Is white chocolate dangerous for dogs? It contains very little theobromine, but the fat and sugar can still cause stomach upset or pancreatitis, so call your vet if a dog eats a large amount.
How big should a guinea pig cage be? Two guinea pigs need at least 7.5 square feet of floor space, and more is better. The Guinea Pig Cage Size Calculator scales for larger groups.
Official references
Pet food labeling and recalls are tracked by the FDA Center for Veterinary Medicine, which also publishes the current list of pet food recalls. Zoonotic disease guidance for pet owners is available from the CDC Healthy Pets program. These calculators are for planning only and do not replace advice from your veterinarian.