Determining fish tank volume has never been easier  with this aquarium calculator you can do it in a blink of an eye. Find water volume 💧 which will fill up your container: choose between 7 typical aquarium shapes  from a simple box, through cylindrical variations, to bow front tanks. If you're wondering what're the formulas to calculate the aquarium size or you're not sure how to use this tool, just scroll down and you'll find the answer below.
If you're looking for the amount of water that goes into a swimming pool, check out our pool calculator.
Aquarium shapes
In our aquarium calculator, we implemented seven popular fish tank shapes:
Name  Aquarium shape 

Rectangular prism  
Cube  
Bow front aquarium  
Corner bow front aquarium  
Cylinder  
Half cylinder  
Quarter cylinder 
Formulas behind the fish tank calculator
If you want to calculate the aquarium size manually, you can use the formulas for volume depending on tank shape:
 Rectangular prism
To find the volume of a standard aquarium, calculate the volume of a rectangular prism (called also the volume of a box):
rectangular = height * width * length
 Cube
Cubeshaped aquarium has the easiest volume equation  simply raise the edge length to the third power:
cube = length³
 Cylinder and its fractions
If you want to calculate the water volume of a cylindrical aquarium, use the formula for cylinder volume:
cylinder = π * (diameter / 2)² * height
Your fish tank is a halfcylinder? No problem, just divide the formula above by 2:
half_cylinder = π * (diameter / 2)² * height / 2
To determine the volume of the quarter of the cylinder, take a fourth part of the full volume:
quarter_cylinder = π * radius² * height / 4
It's handier to use radius instead of diameter in this last case: diameter = 2 * radius
.
 Bow front and bow front corner aquarium
Calculating the volume of the bowfront aquarium is a bit trickier. You need to have given four dimensions: Height, width, length and a full width of the aquarium, and then you can derive the final formula:
bowfront = height * width * length + 0.5 * r² * (α  sin(α)) * height
where α
is a central angle of the circular segment, in radians and r
is a radius of a circle.
α may be calculated as α = 2π  4β
, where β is an angle expressed as tan(β) = 0.5 * length / (full_width  width)
.
For the aquarium with bow front intended to stand in the corner, the formula is:
corner_bowfront = (0.5 * r² * (α  sin(α)) * height) / 2
Aquarium in custom or bizarre shape? Check out our other tools such as triangular prism volume or spherical cap calculator which can find water volume for spherical aquariums, also called fish bowls. Just remember that such tanks are not appropriate for keeping fish and in some countries they're even forbidden! Spherical aquariums are usually small tanks, fish have to swim in circles, what is unnatural for them, and it's hard to put a filter into such tank. Consider a different aquarium shape despite the fancy look of such a tank.
How to use this tool as an aquarium gallon calculator
If you want to calculate how many gallons of water your tank contains, follow these simple steps:

Choose the shape of your aquarium. Assume that you have a bow front fish tank, so select this option from a dropdown list.

Enter the tank dimensions. In our case, we need to type four values. Let's say that the length is 35 in, full width  18 in, width  15 in and height 20 in.

The aquarium calculator finds the volume of your tank. In our case, it's 51.55 gallons.

If you're wondering how much is that in liters, click on the unit name and select the one you're interested  e.g., our aquarium volume in liters is 195.14.
Remember that those calculations may serve as estimations and the result obtained doesn't mean that precisely 51.55 gallons will fit into your tank. We don't take into account e.g. the thickness of the glass or the volume of other objects, such as sand, gravel, filter, plants and... fish. Also, you don't fill up your container completely, do you?
Have a look at another example: how big is a 75gallon aquarium?
You heard that your friend has just bought a 75gallon aquarium. Well, it's hard to imagine, how big is that? Let's check it with this aquarium calculator!

Choose the fish tank shape. We know that our friend is rather a traditionalist, so his obvious choice is a standard rectangular prism tank.

Type the volume  in our case, put 75 gallons into the volume box.
As the given volume may be a result of an infinite combination of the rectangular prism dimensions, we need to put more information into:

Enter two tanks dimensions. Usual height of the aquarium is something between 1826 in, let's say it's 22 in. Additionally, assume the width is the same as height.

We found out that this 75gallon aquarium has ~35.8 in length, so the dimensions are 35.8 x 22 in x 22 in. Quite big, huh? Experiment with different dimensions and shapes to get a better understanding of the concept of volume.