🐠 Aquarium Calculators

About Aquarium Calculators

Our aquarium calculators provide 5 free tools for freshwater and saltwater aquarium hobbyists. Whether you are setting up a new tank or maintaining an established one, these tools help you get the fundamentals right.

Calculating Aquarium Volume

Aquarium volume determines almost every other parameter: stocking density, filtration capacity, heater size, and medication doses. Volume is calculated from the tank's internal dimensions: length × width × height, then converted to gallons or litres. Most aquarium shapes are rectangular, but bow-front and hexagonal tanks require adjusted formulas. As a rule of thumb, the actual water volume is about 80–90% of the total tank volume due to substrate, decorations, and the gap at the top.

Fish Stocking: The "Inch per Gallon" Rule

The classic guideline of "one inch of fish per gallon" is a rough starting point, not a strict rule. It ignores fish body shape (a 6-inch pleco produces far more waste than a 6-inch neon tetra), bioload, territorial behaviour, and oxygen requirements. A more practical approach considers the adult size of each fish, its swimming zone (top, middle, or bottom), its aggression level, and the filtration capacity of the tank. Heavily planted tanks support higher bioloads due to plant-driven nitrogen removal.

Aquarium Heating

Most tropical fish require water temperatures of 24–28°C (75–82°F). A general rule is 5 watts of heater power per litre of water (roughly 3–5 watts per US gallon) for average room temperatures. In colder rooms, or for tanks placed near windows or air conditioning vents, increase heater capacity accordingly. For larger tanks (over 200 litres), two heaters placed at opposite ends of the tank provide more even temperature distribution and redundancy if one heater fails.

Water Changes and Aquarium Maintenance

Regular water changes are the single most important maintenance task in an aquarium. They remove nitrates, replenish trace minerals, and dilute accumulated pollutants. For a moderately stocked tank with good filtration, a weekly change of 20–30% is standard. Heavily stocked tanks or tanks with messy fish may require more frequent or larger changes. The water change calculator helps you determine the exact volume to remove and the correct amount of dechlorinator to add to the replacement water.