About AquaCalc
AquaCalc is a free collection of aquarium calculators built for one purpose: helping fishkeepers make better decisions with simple math. Instead of guessing how many fish a tank can hold, what size heater to buy, or how much water to change, you get a clear answer in seconds.
How our calculators work
Every calculator on this site is based on widely accepted aquarium-keeping guidelines â the inch-per-gallon stocking rule, standard heater wattage recommendations, turnover rates used by filter manufacturers, and the nitrate dilution math behind water changes. We combine these rules with your inputs (tank dimensions, species, room temperature and more) to produce practical recommendations.
Who it's for
Beginners setting up their first tank, and experienced hobbyists double-checking their numbers before buying equipment. If you've ever stood in a fish store wondering "will this fit?" or "is this enough?", these tools are for you.
Important disclaimer
Calculator results are estimates, not professional advice. Every aquarium is different â filtration, plants, feeding habits and maintenance routines all affect what your tank can handle. Always observe your fish, test your water regularly, and adjust as needed. When in doubt, stock lightly and consult experienced aquarists or aquatic veterinarians for health issues.
Free forever
AquaCalc is free to use, supported by advertising. We don't require accounts and we don't sell your data â see our Privacy Policy for details.