Free tools
Animal Calculators
Practical, free calculators for pet owners, breeders and fishkeepers. Each tool shows how it calculates, cites its sources, and explains its limits, so you know how far to trust the result.
Pet and animal calculators
- New
Dog Gestation Calculator
Estimate your dog’s due date from the mating or ovulation date, with a realistic whelping window, accuracy level and week-by-week pregnancy calendar.
- Due date + whelping window
- Week-by-week pictures
- Printable PDF & calendar file
- Dogs
Dog Heat Cycle Calculator
Estimate proestrus and estrus windows and when your dog’s next heat may start, from typical averages.
- Stage windows
- Next-heat estimate
- Merck-based averages
- All pets
Animal Growth Calculator
Predict adult weight and size for puppies, kittens, reptiles and more, with growth milestones.
- Adult size estimate
- Breed presets
- Growth milestones
- Coming soon
Cat Pregnancy Calculator
Due-date estimates and a pregnancy timeline for cat owners.
- Coming soon
Dog Age Calculator
Convert your dog’s age into human-age estimates based on size.
- Coming soon
Animal Gestation Calculator
Compare gestation periods across species, from hamsters to horses.
Aquarium tools
Measure your tank once; every aquarium calculator then works from its real water volume.
- Aquarium Size CalculatorTank volume in litres and gallons for 6 shapes, the real water volume after substrate and decor, and the full weight on your stand.
- Aquarium Filter Flow CalculatorTurnover per hour from your filter’s GPH or LPH, checked against your fish, reef or pond, plus the flow you need and multi-filter totals.
- Aquarium Heater CalculatorHeater wattage from tank size, room temperature and target temperature, with standard sizes and a two-heater split.
- Aquarium Substrate CalculatorHow much gravel, sand or aquasoil to buy for your depth, including sloped scapes.
- Aquarium UV Sterilizer CalculatorCheck if UV suits your problem, find the right flow rate and test your unit against its manufacturer rating.
- Aquarium Light & Photoperiod CalculatorA lighting schedule matched to your plants, light strength and algae situation.
- Fish Tank Size GuidePick your fish and get the minimum and recommended tank size, length and height they need.
- Aquarium Water Change CalculatorLitres or gallons to remove and replace, the new nitrate, ammonia or GH after a change, multi-tank totals and a dated schedule.
- Aquarium Salt CalculatorSalt to add from volume, current and target concentration: freshwater salt, marine mixes, water changes and g/L, ppt or SG.
- Aquarium Evaporation CalculatorDaily water loss, top-off volume and salinity drift for open and lidded tanks.
- GH & KH CalculatorConvert dGH, dKH and ppm, and mix RO and tap water to a target hardness.
- Aquarium Dosing CalculatorScale any product label dose to your real water volume.
- Aquarium Cycling TrackerLog ammonia, nitrite and nitrate and see which stage of the cycle you are in.
- Fish Stocking CalculatorStocking level by species, with warnings for school size, tank size and water needs.
- Fish Compatibility CheckerCheck temperament, size and water overlap for every pair of fish you plan to keep.
- Aquarium Temperature CheckerCheck your water temperature against your fish, shrimp or reef range, with steps if it is too hot or cold.
- Aquarium Problem CheckerCloudy water, gasping fish or white spots: likely causes and safe next steps.
- Aquarium Oxygen CheckerRate your tank’s low-oxygen risk from temperature, stocking and surface movement.
- Aquarium Algae IdentifierIdentify the algae in your tank and fix the cause, not just the symptom.
How we build our calculators
- Published sources only. Formulas come from references such as the Merck Veterinary Manual, the AKC, OATA and NIST, and each tool lists its sources.
- Ranges, not false precision. Results show realistic windows and say how accurate they are.
- Private by default. Calculations run in your browser and your inputs are not stored.
- Not veterinary advice. Calculators support, but never replace, your veterinarian. See our disclaimer and sources.
