Aquarium Volume Calculator with Houston Aqua
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 bowfront 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 that is in liters, click on the unit name and select the one you're interested in – 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 that is. 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 in 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 input more information.

Enter two tank dimensions. The usual height of the aquarium is something between 1826 inches; let's say it's 22 inches. Additionally, assume the width is the same as the 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.
FAQ
How do I calculate the volume of an aquarium?
The volume of an aquarium is the same as that of any other object. You require the dimensions to estimate the volume.
The length, width, and height are the parameters on which the volume of most shapes depends, except for cylindrical shapes. They require the diameter or radius to estimate the capacity of the object.
Does shape of the aquarium impact its volume?
Yes, it does. Every shape has a different volume. And most of them have a different formula to calculate the volume.
For instance, the volume of a rectangular shape depends on the length, width, and height, or a cube needs only length, whereas cylindrical objects require diameter and length to estimate the volume.
How many fish can I put in my 50 liter aquarium?
The number of fish you can put in 50liter aquarium is 1617. The general estimation is 1 liter of water for 1 centimeter of fish.
However, the setup of your tank will define how many fish you able to have . We recommend to set your tank up with lots of plants so the fish feels comtable and it also helps you with your water quality . Lastly, be aware that filtration also plays a large part in how many fish your aquarium will support. Your filter should run four times the total volume of water in the tank through the filter each hour. That means a 10gallon tank requires at a minimum a filter rated at 40 gallons per hour. If in doubt, go higher, as there is no danger of overfiltering your water.
Suppose your fishes are 3 cm in size. Follow the steps to count the number of fish:

Note down the volume of your aquarium in liters.

Estimate the size of your fish in centimeters.

Divide the volume by the size.

The result is the number of fish.
So,
50/3 = 16.66
. Round this result to 17 because you can't have half a fish.
How many gallons of water can a 3 m³ aquarium hold?
A 3 m³ aquarium can hold 792.5 gallons of water, which is equal to 3 000 liters. The m³, gallons, and liters are all units to measure the volume of a container. Here's how to convert between these units:
1 m³ = 1000 liters
and
1 liter = 0.264172 US gallons