Aquarium Volume Calculator

Multiply the interior length, width, and height in inches, then divide by 231 (the number of cubic inches in one US gallon). For metric measurements, multiply length, width, and height in centimetres and divide by 1,000 to get litres. Always measure the inside of the glass rather than the outside, because trim and glass thickness inflate external dimensions.

Labeled capacity can differ from usable water volume due to factors like tank construction (glass thickness, frame), intended fill level (leaving freeboard to prevent overflow), and displacement from substrate, rocks, and equipment. Manufacturers may specify volume differently, so it's best to measure your tank's interior dimensions for accurate calculations.

Always follow the specific medication label instructions. When the label calls for dosing by water volume, use the actual/net water volume it specifies. For example, treating a 50 gallon tank that really holds 42 gallons means you would overdose by nearly 20% if you used the gross volume. This illustrates why accurate water volume matters. This calculator shows an estimated net volume (90% of gross) alongside the gross figure as a reference.

For a cylinder, use the circular area formula: pi times the radius squared, multiplied by the height. For a bowfront, the calculation is an approximation based on assumed curvature; the curved pane adds roughly 20-25% to the average depth, so the calculator averages the front and back depth rather than treating it as a plain rectangle. Select the matching shape above and the correct formula is applied automatically.

A common guideline is four to six times tank turnover per hour, so a 50 gallon tank suits a filter rated around 250 gallons per hour. Planted tanks often run at the lower end to avoid disturbing CO2 distribution, while messy, heavily stocked, or marine systems benefit from the higher end. The calculator reports 5× tank turnover as a starting-flow guideline.

Fresh water weighs about 8.34 pounds per US gallon, or 1 kilogram per litre. Saltwater is slightly denser at roughly 8.55 pounds per gallon. Water alone is the bulk of a filled tank's mass, which is why a 55 gallon aquarium carries roughly 459 pounds of water before you add glass, substrate, and equipment. Use the tank weight calculator to estimate the full loaded mass.

To convert gallons to liters, multiply the volume in gallons by 3.785. For example, a 10 gallon tank is approximately 37.85 liters. This calculator provides volume in both gallons and liters for your convenience.

Net (usable) water volume is less than gross volume due to displacement from substrate, rocks, decorations, equipment, and the fact that tanks are often not filled to the brim. This calculator uses a 90% gross-volume estimate as a rough starting point for calculations, not a measurement of your tank's actual water volume.

Use our aquarium volume calculator by entering your tank's length, width, and height in inches to get the volume in gallons.

For a rectangular tank: Volume (gallons) = (Length × Width × Height) / 231. For other shapes, use the appropriate geometric formula.

One cubic foot of water is approximately 7.48 gallons.

Calculate using the actual water height instead of the full tank height in the volume formula.

A nominal 55-gallon tank's actual volume varies by dimensions; measure your tank and use the calculator for precise volume.

Similarly, a nominal 75-gallon tank's actual volume depends on its exact length, width, and height; use the calculator for accuracy.