Aquarium Volume Calculator
Use our free aquarium volume calculator to convert your tank’s dimensions into an accurate water volume in gallons or liters. Also known as a fish tank volume calculator, aquarium capacity calculator or gallon calculator, it handles rectangular, cube, cylinder, half-cylinder, hexagon, bow-front, corner-pentagon and L-shaped aquariums.
For a standard rectangular tank, volume is simply length times width times height in inches, divided by 231 (the number of cubic inches in a US gallon). Keep in mind that your true water volume is always a little less than the tank’s rated size once you account for substrate, rock and the gap below the rim — so use your measured water level for the most accurate dosing and stocking numbers.
Formula: Gallons = (L × W × H in inches) ÷ 231 • Cylinder: (π × r² × H) ÷ 231
Estimate your tank volume
Rectangle
Cube
Hexagon
Octagon
Flat Back Hexagon
Cylinder
Half Cylinder
Corner Cylinder
Elliptical
Corner Pentagon
L-Shaped
Corner Prism
Frequently Asked Questions
How do I calculate the volume of my aquarium?
Multiply the length, width and height of the water area in inches, then divide by 231 to get US gallons. For example, a 24 by 12 by 16 inch tank is 4,608 cubic inches divided by 231, or about 20 gallons. Cylindrical tanks use pi times the radius squared times the height, divided by 231. This calculator applies the right formula for each of a dozen tank shapes automatically.
Why is my actual water volume less than the tank’s rated size?
A tank rated at 75 gallons rarely holds 75 gallons of water. Substrate, live rock, the space below the rim and equipment displacement all reduce the real water volume, often by 10 to 20 percent. For accurate dosing and salt mixing, base your calculations on measured water volume rather than the label on the box.
How do I convert aquarium liters to gallons?
Divide liters by 3.785 to get US gallons, or multiply gallons by 3.785 to get liters. This calculator switches between imperial and metric with a single toggle, so you can work in whichever units you prefer.
