March 7

Determine Water Volume with an Aquarium Calculator


A fish tank always stands out, whether in public aquariums or as a house to your colorful pet. However, before you go out and buy your own, it is crucial to understand tank shapes and how to use an aquarium calculator to determine the water volume you require.

Depending on the number of fish and space available, aquarium tank sizes can fit between 0.5 to over 200 gallons of water.

In this article, we’ll take a look at the importance of tank volume and shape before we answer “how to calculate water tank capacity in gallons” using one of our favorite calculators.

Aquarium Shapes and Capacity

aquarium shapes

Did you know different breeds of fish prefer different aquarium dimensions and sizes? For example, energetic fish like barbs and danios require a lot of horizontal space.

On the contrary, a wide bottom area is essential for territorial fish, so it’s best to avoid narrow or tall aquariums. 

There are many unique aquarium shapes, including cylindrical and hexagon fish tanks. Some variations include cubes, bow front, or corner bow aquariums.

The most popular choices to date remain the glass bowl and rectangular tanks with varying dimensions to gallons

Small Aquariums or Fishbowls

Although a smaller fish tank is easy to maintain, it can only hold up to 1.5 to 5 gallons of water. Thus, a round aquarium or bowl doesn’t have the surface area required for healthy gas exchange and is vulnerable to harmful build-up.

As a result, this can alter the water’s pH levels, making it unsafe for your fish.

While they seem the best for beginners, compact fish tank dimensions can only accommodate one or two small fish. Most species quickly outgrow their bowl, leaving owners wishing they had started with larger fish tank sizes.

5 to 10 Gallon Tanks

A small rectangle or cylinder aquarium containing approximately 5 to 10 gallons of water is considered ideal for most homes and apartments. The tank dimensions required for this volume of water don’t take up much room.

Furthermore, they are large enough to accommodate several fish, filtration devices, and aquarium heater size

But a ten-gallon fish tank also comes with its own set of problems. Filtration and pH levels have to be closely monitored owing to their open design, small size, and limited surface area.

They also need to be cleaned regularly.

10 to 20 Gallon Tanks 

Aquariums that hold between 10 and 20 gallon high dimensions are a great option for fish owners who want a manageable tank. You can find ornamental designs such as a cylinder tank as décor and adorn them with aquatic plants or decorative pieces.

    Nevertheless, this tank volume also requires constant monitoring to ensure chemical balance and proper filtration. 

    20 and More Gallons 

    You can house dozens of fish while assuring they have enough room to swim around and stay healthy. Aquariums that are 20 or more gallons add a touch of refinement as they are heavier and larger than smaller ones.

    A 40-gallon fish tank or larger can host other aquatic creatures such as algae alongside fish. However, the larger the aquarium, the more costly and time-consuming maintenance is.

    Additionally, you may require structural reinforcements or stands.

    How Many Fish per Gallon? 

    As a general rule of thumb, you should use at least one gallon of water for every inch of fish. Unfortunately, this guideline doesn’t take into account water surface area, natural habitat, and physical features of the species, such as shape, growth, and activity levels.

    Moreover, some species are hostile and can’t live with other fish.

    So, is there an aquarium calculator that can solve this problem? Sadly, there is no accurate “how many fish in a tank” calculator.

    The only way to create a secure and comfortable environment for your marine life is to conduct extensive research for their breed.

    For example, it is recommended that all tanks hold at least 5 gallons of water for a single fish, but goldfish require at least 20 gallons of water for every two fish.  

    Considering some fish can grow to enormous sizes, it’s always advisable to size up on the fish tank size chart

    Why is it Important to Calculate Tank Volume? 

    Having too many fish in a small tank can quickly result in chaos. Several issues can arise when fish don’t have the space to grow and move comfortably.

    Stunted growth, spinal deformities, and muscle atrophy are some of the many developmental health problems commonly seen in such fish. The life span of undersized fish is also drastically short!

    Fish are territorial and need their hiding spots when forced to coexist. Using a tank capacity calculator establishes enough room for tank mates to avoid each other. If your aquarium does not have adequate water, you can expect to see aggression.

    Further, it’s easier for healthy fish to fight off stress when relaxed in their surroundings. Distress includes gulping air, not eating, and developing skin or behavioral diseases which can spread to other fish. 

    Ammonia is a byproduct of fish waste, and bacteria convert it into nitrates. As a result of the breakdown of ammonia, the tank features a less-toxic environment and better water quality.

    Unless frequent water changes and gravel vacuuming are carried out, this can wreak havoc. Without a volume finder, it’s impossible to care for your aquarium correctly. 

    Therefore, figuring how many gallons are in a tank is a vital step to keep your pet thriving. An aquarium calculator can help determine the amount of space and filtration your fish species require.

    Using Formulas to Calculate Aquarium Gallons 

    tank size

    One of the most commonly asked questions by fish owners is, “how big is your tank?”. For the most part, people either forget or don’t know how to calculate the volume of their tank. 

    If you want to calculate tank dimensions instead of using an aquarium calculator manually, you need to measure it with a tape measure to get its length, width, and height in inches. Then, use the corresponding formula to calculate the volume. 

    Depending on the shape, you’ll need a different formula for bow-front, cylindrical, rectangular, and other aquariums. 

    Rectangular or Cube Tanks 

    To calculate the volume of a rectangular prism, also known as standard aquariums, multiply the height, width, and length. 

    Rectangle = height x width x length

    Cube-shaped aquariums are the easiest to calculate without an aquarium calculator. First, measure the edge length and raise it to the third power.

    Cube/ Box = length³

    Cylinder Tanks and its Fractions 

    For cylindrical tanks, you can substitute that value of π with the number 3.142. 

    Cylinder = π x (diameter/2)² x height

    If you have a half-cylinder, divide the answer by two. Similarly, if your aquarium is a quarter cylinder, you can replace the diameter with the radius instead. 

    Quarter Cylinder = (π x radius² x height)/4

    Complex Shaped Tanks

    Is your aquarium custom-built or in a unique shape like a corner or front bow? Calculating the volume of such shapes is trickier and requires advanced calculations.

    Check out how to use our recommended aquarium calculator below. 

    Use Aquarium Calculator to Find the Volume

    Aquarium Tank Volume Calculator


    Follow these steps to use Aquarium Calculator to determine the volume of your fish tank:

    Tank Shape

    Decide on the overall shape of your aquarium. Then, select from the rectangular, bow-front, pentagon, or other options on the top of the Inch Calculator. 

    Size or Measurements

    Using the measurements you record from your tape measure, enter your aquarium’s length, width, height, or diameter. The aquarium calculator requires different values depending on the shape you select. 

    Calculate Volume of Tank

    Hit “Calculate .”The aquarium calculator will give you an answer in gallons and liters.  

    If you’re wondering what the answer in cubic inches is, you can convert the volume to gallons by dividing it by 231.

    Other Factors to Consider 

    It’s vital to keep in mind that these figures are only estimates. A water volume calculator relies on only internal dimensions to come up with approximate inches to gallons volume.

    However, this doesn’t consider factors like glass thickness and water operating height which require additional tools like an aquarium glass thickness calculator.

    Likewise, the displacement of water from rocks, décor, filters or even fish affects the calculation. By subtracting these from the estimate, you can obtain the exact total operating volume.

    Even then, an online aquarium calculator is an excellent way to determine your tank requirements. 

    Get Calculating! 

    Working with numbers isn’t everybody’s strength. Thus, when trying to figure out how to calculate gallons in a tank, an aquarium calculator can make things easier.

    Determining the volume of your tank can extend the lifespan of your fish reduce maintenance so you can enjoy your pets. All you need is a tape measure to get started! 


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