🐠 Aquarium Calculator
Enter your tank’s inside dimensions to calculate its water volume in liters and gallons, plus a rough stocking guideline.
What this calculator does
This calculator finds the water volume of a rectangular aquarium from its length, width, and water height, and converts that volume into liters and both US and Imperial gallons.
How the calculation works
Volume is simply length times width times height. In metric units this gives cubic centimeters, which converts directly to liters by dividing by 1,000; liters are then converted to gallons using standard conversion factors.
The stocking guideline uses the traditional freshwater ‘one inch of fish per gallon’ rule of thumb — it’s a rough starting point for small community tanks, not a precise or universal rule, since actual stocking depends on fish species, adult size, and filtration.