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Aquarium Calculator

Aquarium Calculator

Select the aquarium shape and input its dimensions to estimate the number of gallons required to fill it up through this calculator.


Select Tank Shape:







Front Pane




Radius 1


Radius 2


Length Long side


Length Short side


Length 1


Length 2


Width 1


Fill Depth



Width 2


End Pane


Full Width


Triangle Image

Table of Content

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Make use of this aquarium calculator that will let you calculate volume of fish tank. Yes, if you find it hard to estimate how much water you need to fill up your tank, then do not worry! Our online fish tank volume calculator will readily do this for you.

Let’s go deeper in the content below to know different shapes of the aquarium and formulas to calculate the water volume for each shape respectively.

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What Is Aquarium Volume?

Aquarium volume corresponds to the volume of water that it can hold. It is basically determined by taking the following dimensions into considerations:

  • Aquarium length (Side by Side Measurement)
  • Height of Aquarium (Top to Bottom Measurement)
  • Aquarium Depth ( Front to Back Measurement)

The online aquarium volume calculator also keeps in pace these parameters while performing aquarium volume calculations.

Water Volume In Aquarium:

Basically, there are two types of volume that are described below:

Theoretical Volume:

This volume corresponds to the full sized capacity of the aquarium. Most of the time, the manufacturers mention this volume on every aquarium so as to easily estimate the volume of the water it can hold. For further help, you may subject the aquarium calculator to better estimate the results.

Realistic Volume:

The realistic volume of the fish tank is a far better estimation to take into consideration while buying an aquarium. This volume is always less than the full capacity of the tank as it allows smooth running of the water in each and every corner and creates a healthy ecosystem for the fish.

Different Shapes of Aquarium:

As discussed previously, aquariums come in different shapes, sizes, and dimensions. But this aquarium dimension calculator uses different equations to calculate aquarium gallons needed to fill the box. The most in demands along with their formulas are given as under:

Rectangular Prism Shape:

rectangular fish tank
Rectangular = Height * Width * Length

Cubic Shape:

cubic fish tank
Cube = Length^3

Regular Hexagonal Shape:

For a regular hexagon, each side is of the same length. So we have:

Volume = ((3*√3)/2) * Front Width² * Height

Flat Back Hexagon Shape:

flat back hexagonal fish tank
Volume = (((((3*√3)/2) * front width²)/2) + (side * length)) * height

In our fish tank calculator, you can select these two shapes separately to calculate volume of fish tank.

Octagonal Shape:

octagonal fish tank
Volume = (2 * (front width²) * (1+√2)) * height

Cylindrical Shape:

cylindrical fish tank
Aquariums come in different cylindrical patterns. For each particular one, the equation to find the volume of the water is given as below:

Regular Cylinder:

Cylinder = π * (Diameter / 2)^2 * Height

Half Cylinder:

half cylindrical fish tank
Half_Cylinder = π * (Diameter / 2)^2* Height / 2

Quarter Cylinder:

quarter cylindrical fish tank
Quarter_Cylinder = π * Radius² * Height / 4

We recommend you use the radius of the shape in order to make the computations faster and easier.

Diameter = 2 * Radius

Bow Front Shape:

bow front fish tank
To calculate volume of the bow front aquarium, you require the following dimensions:

  • Height
  • Width
  • Length
  • Full cross sectional width

All of these factors are covered in the following expression:

Bowfront = Height * Width * Length + 0.5 * r^2 * (α – sin(α)) * Height


  • α = Central angle
  • r = Circle section radius

L Shaped Tank:

L shaped fish tank
Here one tricky thing that you will mostly cope with is the shape itself. In an L shaped tank, we have a couple of rectangles joined. Here, you need to calculate the area of both of these rectangles separately. After that, add the areas together and multiply the result with the height. The whole parameters are covered in the following formula that are also used by this aquarium volume calculator to determine the outputs:

Volume = ((Length 1 * Width 1) + ((Length 2 – Width 1) * Width 2)) * Height

Elliptical Shape:

elliptical fish tank
Volume³ = 𝛑 * radius 1 * radius 2 * height

Corner Pentagon Shape:

corner pentagonal fish tank

Corner Prism Tank:

corner prism fish tank
Volume = ((Length 1 * Length 2)/2) * Height

Aquarium Weight:

You should keep in mind that:

  • At a temperature of about 4 degrees celsius, a gallon of fresh water weighs about 8.3454 at a gravity of 1.000.
  • Also at the specific gravity of 1.025, the weight of one gallon containing salty water is about 8.54 pounds.

For instance, we have arranged tables below that are arranged properly, depending upon the quantity, weight, volume, and condition of water. Let’s look at these one by one!


Tank Size L x W x H Empty Weight Plants & Rocks Filled Weight Freshwater (Including Plants & Rocks) Filled Weight Saltwater (Including Plants & Rocks)


Inches lbs lbs lbs


2 1/2 gallon 12″ x 6″ x 8″ 3 3 26.9


5 gallon

16″ x 8″ x 10″ 7 10 58.7 59.8
10 gallon “Leader” 20″ x 10″ x 12″ 11 15 109.5


15 gallon

24″ x 12″ x 12″ 21 25 171.2 174.3
15 gallon High 20″ x 10″ x 18″ 22 25 172.2



Tank Size L x W x H Empty Weight Plants & Rocks Filled Weight Freshwater (Including Plants & Rocks)

Filled Weight Saltwater (Including Plants & Rocks)


Inches lbs lbs lbs lbs
20 gallon High 24″ x 12″ x 16″ 25 30 221.9


20 gallon Long

30″ x 12″ x 12″ 25 30 221.9 226.1
25 gallon 24″ x 12″ x 20″ 32 40 280.6


29 gallon

30″ x 12″ x 18″ 40 45 327 333.1
30 gallon Breeder 36″ x 18″ x 12″ 48 48 346.4


40 gallon Breeder

36″ x 18″ x 16″ 58 60 451.8 460.2
40 gallon Long 48″ x 12″ x 16″ 55 60 448.8



Tank Size L x W x H Empty Weight Plants & Rocks Filled Weight Freshwater (Including Plants & Rocks)

Filled Weight Saltwater (Including Plants & Rocks)


Inches lbs lbs lbs lbs
50 gallon 36″ x 18″ x 19″ 100 70 587.3


55 gallon

48″ x 13″ x 21″ 107 75 641 652.5
65 gallon 36″ x 18″ x 24″ 126 90 758.5


75 gallon

48″ x 18″ x 21″ 140 110 875.9 891.6
90 gallon 48″ x 18″ x 24″ 160 120 1031.1


125 gallon

72″ x 18″ x 21″ 206 130 1379.2 1405.3
150 gallon 72″ x 18″ x 28″ 338 140 1729.8


180 Gallon

72″ x 24″ x 25″ 350 170 2022.2 2059.7
225 Gallon 72″ x 27.5″ x 27.5″ 360 190 2427.7


You can yourself verify these results by this aquarium size calculator free of cost and in seconds.

How Aquarium Calculator Works?

Let’s go by the guide below that is particularly arranged to let you know how to operate this fish tank calculator!


  • From the first drop-down list, select the shape of the tank
  • After that, enter the necessary dimensions of the selected shape in their designated fields
  • Once you are done with the stuff, tap the calculate button


The free fish tank gallon calculator does the following calculations:

  • Calculate aquarium gallons
  • Volume of the aquarium in various units of measurements


What is the most important factor having a successful aquarium?

One of the major facts that an aquarium owner must care for is the water quality. Yes, you would not believe but the water is the component that is responsible for longevity of life or death for fish. Poor water may have poisonous particles in it and it is fatal for fish life. That is why you must go by changing the water every other day to keep your pet healthy. Moreover, you should also employ the aquarium calculator to calculate the water quantity sufficient to fill your tank and thus keeping your fish alive for long.

What happens if fish tank is too small?

If you are nourishing a juvenile fish in your aquarium tank, then a small fish tank would cause some serious issues to your fish including:

  • Stunted growth
  • Spinal deformities
  • Atrophied muscles

Are bigger aquariums easier to maintain?

Yes, definitely! A large fish tank provides a proper ecosystem with an in-built facility of self-cleaning. That is why the huge water volume and temperature remains stable enough to keep the environment life-friendly for your fish.

How many gallons in my aquarium are?

It depends upon the size of the aquarium. When buying the tank, it is recommended to use this aquarium gallon calculator first to estimate the tank size you need to buy. After that, go for relating this result value with that fish tank size\s written on a sticker pasted on them.

Which size is best for aquarium?

The best size of the aquarium is to utilise a gallon of water per inch of a fish. To take instant assistance in this regard, we suggest you use this aquarium calculator.

Do fish get bored in small tanks?

Yes! Fish become very annoying while kept in small bowls or tanks. That is why you should go for selecting a reasonable fish tank and use a water pump in order to continue the flow of water.

Does aquarium air pump size matter?

Yes it does! In actuality, you must always choose the size of the pump bigger than the suggested. Let us take an example! If you buy an aquarium with a capacity of 80 gallons, you must buy a pump that is good to flow water of about 100 gallons.

How can I improve the water quality in my aquarium?

Following are some precautionary measures that you should follow if looking to maintain water quality in aquarium:

  • Always use purified water
  • Never go for over-feeding your aquarium
  • Change chemical filter media in it
  • Keep on changing the water every other or couple of days

Can you have too much filtration in an aquarium?

If you install a filter in a fish tank, you must cope with the fact that water is passing at the rate of 4 times/hour from it. Otherwise, it will be speedy, pushing the fish away again and again, and thus creating an awkward environment for the fish.

How many fish can you have in a 100 Litre tank?

There are exactly 22 gallons of water in a 100 litre tank that could also be checked by using the online aquarium calculator. Anyways, coming to the point, a 100L tank can accommodate about 22 fully grown fish.


Determining the volume of aquariums is not such an easy task. You will always have to look for the tanks that are more durable, strong to hold the maximum volume of water in it. And keeping in view these hurdles, you must go by utilising this aquarium calculator so as to estimate the fish tank size that would suit your choice.


From the source of Wikipedia: Aquarium, Antiquity, Aquarium filter, Materials suitable for aquarium filtration, Types