Aquarium calculators
Four free calculators for tanks that are not a standard size, or for checking a plan before you buy. They run in your browser; nothing you enter is sent anywhere.
How they work
The volume, weight and substrate calculators use plain geometry and published densities: 231 cubic inches to the US gallon, 8.34 pounds per gallon of fresh water, and typical dry densities for gravel, sand and soil. Each page writes out its formula and a worked example so you can check the arithmetic.
The stocking calculator uses adult sizes, minimum tank footprints, temperature and pH ranges from Seriously Fish species profiles, with a few species filled in from other sources. Its load model is our own, described in full on the page, including what it cannot tell you.
Which one to use
- Planning which fish to buy: the stocking calculator. It checks tank size, group size, temperature, pH and temperament together.
- Dosing medicine or conditioner: the volume calculator, with your real water line and gravel depth, so you dose for the water actually in the tank.
- Buying a stand or placing a tank upstairs: the weight calculator, which also gives the load per square foot on the floor.
- Buying gravel, sand or soil: the substrate calculator, which works from the footprint rather than the gallons.
Standard tanks are already worked out
If your tank is a standard size, its page already shows the volume, empty and filled weight, heater, filter, stand and lid sizes, and which popular fish fit. Start from the size chart.