A clearer picture of your tank
Aquarium Volume Calculator
Find your rectangular aquarium’s capacity and water volume in US gallons or liters. Account for the water level and, if needed, the space taken up by solid material.
H is tank height. WH is water height, measured from the inside bottom to the water surface.
Measure your aquarium
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Aquarium capacity and actual water volume
The tank’s full capacity uses its inside length, width and total inside height. The amount of water uses the actual water height instead. Space above the waterline is not included in that water volume.
Full capacity
V = L × W × H
Geometric volume up to the top of the tank.
Volume at the waterline
V = L × W × WH
Volume below your selected water level, before subtracting solid displacement.
Water after displacement
Water volume = volume at WH − displacement
An estimate when the displacement allowance is estimated.
Example: a 100 × 40 × 45 cm aquarium
Full capacity is 100 × 40 × 45 ÷ 1,000 = 180 L. If the water height is 40 cm, the volume below the waterline is 160 L. An entered displacement allowance of 12 L leaves an estimated 148 L, or approximately 39.10 US gallons.
A chosen 25% water change is then 148 × 0.25 = 37 L, or approximately 9.77 US gallons.
Measure the inside of the tank
- Measure the clear inside length and width, rather than outside glass dimensions.
- Measure H from the inside bottom to the top of the usable tank space.
- Measure WH from that same bottom to the water surface. An empty WH field uses H; a value of 0 represents an empty tank.
- Use one length unit for every dimension. The example illustration shows what to measure; it does not change with your inputs.
Allowing for gravel, rocks and decorations
The calculator does not assume a standard amount of displacement. Leave the setting at “No allowance”, enter your own percentage estimate, or enter a displaced volume in liters or gallons.
For a percentage allowance, the percentage applies to the volume below WH. For example, 10% of 160 L subtracts 16 L. Known volume mode subtracts the volume you enter.
Water fills spaces between gravel grains and around decorations. The geometric volume of an entire gravel layer is therefore not necessarily the amount of water it displaces. Count the submerged solid material and avoid subtracting empty space above the waterline twice.
For a more accurate water-volume figure, measure the amount of water added while filling the aquarium. A geometry-based estimate depends on your measurements and the displacement allowance.
US gallons and Imperial gallons
| Unit | Liters |
|---|---|
| 1 US gallon | 3.785411784 L |
| 1 Imperial gallon | 4.54609 L |
The main result defaults to US gallons. Both gallon systems are labeled explicitly, and the result also shows the equivalent values in the other units.
Water-change amounts
The water-change result multiplies the calculated water volume, after any displacement allowance, by your chosen percentage. It uses the water currently represented by WH rather than the full empty-tank capacity.
This form covers rectangular aquariums. For a cylindrical container, use the cylinder volume calculator. For general container dimensions, use the box volume calculator.
Displayed values are rounded. Calculations use unrounded values and the defined length and liquid-volume conversions.