Aquarium calculators
Ten calculators for the questions every tank runs into, answered with real numbers — from sizing the tank and gear to water changes, cycling and running cost.
Plan & size your tank
Start here: how big it is, how heavy it will be, and the gear it needs.
Aquarium volume calculator
How many gallons is your tank? Dimensions in, volume and water weight out — the number every other decision starts from.
Open the tool →Heater wattage calculator
Size the heater from tank volume and the temperature rise over your coldest room temp, with the reviewed heaters that cover it.
Open the tool →Filter GPH calculator
Work out the filter flow rate (GPH) your tank needs, with real-world headroom for hang-on-back derating.
Open the tool →Substrate calculator
How much gravel or sand your tank needs, from footprint and depth — in pounds, kilograms and litres.
Open the tool →Aquarium weight calculator
The total filled weight — water, substrate, rock and the tank itself — so you can check your stand and floor.
Open the tool →Water & maintenance
Keep the water right, from the first fishless cycle to every weekly change.
Fishless cycle ammonia calculator
How much household ammonia to dose to hit your target ppm — a starting dose to test and adjust, with the cycling guide alongside.
Open the tool →Water change calculator
The exact percentage and gallons to change to hit your target nitrate, plus the tap-water catch to watch for.
Open the tool →Water conditioner dosing calculator
The exact dose of Prime, API, Fritz and more for your water volume, from each maker's own stated rate.
Open the tool →Stocking & running cost
How many fish it holds, and what it costs to keep running.
Stocking calculator
A realistic estimate of how many fish your tank can hold, by tank and adult fish size — not the one-inch-per-gallon myth.
Open the tool →Electricity cost calculator
The monthly and yearly running cost of a heater, filter or light — with the heater duty-cycle reality built in.
Open the tool →