🐠 Aquarium Volume
Gallons and liters for any tank size
About this calculator
Aquarium capacity decides everything from stocking levels to heater size. Enter your tank's length, width, and height in inches or centimetres and the calculator returns volume in litres and US gallons — with a realistic fill level around 90 percent, since nobody fills to the brim.
Volume is length × width × height, converted: 1 US gallon equals 3.785 litres. The classic stocking guideline is about 1 inch of adult fish per gallon, adjusted down for messy or territorial species — volume also tells you the water weight, roughly 1 kg per litre, which matters for the stand.
Tip: Cycle the tank before adding fish — a new aquarium needs 2 to 6 weeks for beneficial bacteria to establish, or ammonia from the first fish can turn the water toxic.