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Aquarium Volume Calculator: How To Easily Find Your Tank’s Water Volume

How can you easily and accurately find the volume of water in your tank? A good aquarium volume calculator should match the shape and account for any objects in your tank.

By Andy Birks
Last updated on

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I’ve had lots of tanks over the years, and while figuring out the water volume in a rectangular tank is straightforward forward it can be difficult with other tank shapes. An aquarium volume calculator can make life a lot easier if you have a bow front or double bullnose for example. 

And it can be important to get it right if you are administering any medication or figuring out how many fish to stock in your tank.

Many aquarium volume calculators online have a good range of shapes but crucially lack the ability to account for any objects you have in your tank. I set out to change that.

So if you want to get an accurate estimate for the water volume in your aquarium, whether straight-lined, curved, or corner tank, then read on to find out how!

How To Use The Aquarium Volume Calculator

  1. Choose the shape of your aquarium. Choose from our aquarium volume calculators for tanks with straight lines, curved tanks, or corner tanks below.
  2. Enter your tank dimensions. Use the diagram against each calculator to help you enter your measurements. Any additional instructions are shown under the appropriate field.
  3. Include the weight of any tank objects. This step is optional but makes for a more accurate volume calculation. Just weigh anything that is going into your tank, and enter an overall total weight. It could include rocks, driftwood, or even your filter!
  4. Click outside the input fields when done. Our aquarium volume calculator will automatically calculate the volume once you have finished filling in your measurements. You don’t have to press ‘calculate’. Just click outside of the input fields to see the volume update.

Aquarium Volume Calculator For Tanks With Straight Lines

Choose the shape that closest resembles your tank. Or try our curved tanks or corner tanks calculators further down the page.

Aquarium Volume Calculator For Tanks With Curves

Choose the shape that closest resembles your tank. Or try our corner tanks calculator further down the page.

Aquarium Volume Calculator For Corner Tanks And Fishbowls

Choose the shape that closest resembles your tank. Or try our straight line tanks or curved tanks calculators further up the page.

Aquarium Volume Calculator FAQs

Why Might I Need To Know The Volume Of My Tank?

There are a couple of very good reasons why you might need to know the water volume of your aquarium. This applies whether you are starting a freshwater or custom saltwater aquarium:

  • Understanding the dosage levels needed for medication. If you encounter any diseases in your tank it’s very important to get the dosage for medication right. The more accurately you can calculate the water volume in your tank the better.
  • Stocking levels. The more accurately you know your tank’s volume the more aware you can be of how many fish you can keep safely without overstocking.
  • Water maintenance and changes. Knowing the water volume of your tank is a key factor to help drive when to do your water changes and tank maintenance.

How Can I Make My Measurements More Accurate?

  • Measure to the fill line! When measuring the height of your tank try to measure to the water line rather than all the way to the top of the tank. If you have a layer of substrate at the bottom of your tank you should also measure from the top of that layer.
  • What about glass thickness? For most domestic tanks, the thickness of the glass won’t really have a great effect on the volume calculation. But do try to take your measurements from inside the tank to account for glass thickness.
  • The sides of my aquarium are tapered! If your tank has tapered sides try to take width measurements at the mid-distance between the water line and the top of the substrate.

How Does The Aquarium Volume Calculator Account For Tank Objects?

Our aquarium volume calculator allows you to enter an overall weight for the objects in your tank. This is subtracted from the initial volume to give the final volume.

We do this by using the following factors for imperial measurements:

  • 1 pound (lbs) of water = 0.12 US gallons [1]

So where you enter in pounds we multiply by 0.12 before removing this result from the initial volume.

What Are The Formulas Used In The Aquarium Calculator?

If you want to check calculations manually or understand more about how our aquarium volume calculator works you can find the formulas for all of them below.

But notice that all of them give the cubic volume (volume³). To find the volume in US gallons we use the following factor:

  • 231 cubic inches (in³) = 1 US gallon [2]

So to give the volume in US gallons we divide the cubic volume (in³) by 231.

Formulas For Tanks With Straight Lines

  1. Rectangular Prism or Cube: 
    • Volume³ = length * width * height [3]
  2. Hexagonal Tank:
    • Volume³ = ((3*√3)/2) * front width² * height [4]
    • This is for a regular hexagon, so each side panel must be the same size.
  3. Flat Back Hexagon:
    • Volume³ = (((((3*√3)/2) * front width²)/2) + (side * length)) * height
    • This uses the formula for a regular hexagon but divides by two to give the front section. The back section uses the formula for a rectangular prism.
  4. Octagonal Tank:
    • Volume³ = (2 * (front width²) * (1+√2)) * height [5], [6]
    • Again, this is for a regular octagon. Each side panel must be the same size.
  5. L-Shaped Tank:
    • Volume³ = ((length 1 * width 1) + ((length 2 – width 1) * width 2)) * height
    • This calculation splits the L shape into two rectangles to calculate their areas. It then adds them together before multiplying by the height. So you need to make sure you insert the correct lengths and widths in the right parts of the calculator as the diagram shows.

Formulas For Tanks With Curves

  1. Bow Front Tank: 
    • Volume³ = (((𝛑 * (length/2) * (full width – width))/2) + (length * width)) * height
    • This calculation uses the formula for half an ellipse for the bow front [7], along with a rectangular prism at the back.
  2. Cylindrical Tank:
    • Volume³ = (𝛑 * radius²) * height [8]
    • To make things easier to measure, we ask you to include the full diameter and our calculator divides it by two to get the radius.
  3. Half Cylinder Tank:
    • Volume³ = ((𝛑 * radius²) * height) / 2
    • This is exactly the same as the cylinder, but with a simple divide by two to get the half cylinder!
  4. Elliptical Tank:
    • Volume³ = 𝛑 * radius 1 * radius 2 * height [9]
  5. Double Bullnose Tank:
    • Volume³ = ((𝛑 * (width/2) * ((full length – length)/2)) + (length * width)) * height
    • This is very similar to the calculation for a bow front tank. But here we use the formula for a full ellipse to account for each curved end of the tank.

Formulas For Corner Tanks

  1. Corner Cylinder Tank: 
    • Volume³ = ((𝛑 * radius²) * height) / 4
    • This is simply the formula to calculate the volume of a cylindrical tank but divided by four.
  2. Corner PentagonTank:
    • Volume³ = (length² – ((length – end pane)² /2)) * height
  3. Corner Prism Tank:
    • Volume³ = ((length 1 * length 2)/2) * height [10]
    • This formula calculates the area of a triangle before multiplying by the height.
  4. Fishbowl Or Spherical Tank:
    • Volume³ = (4/3) * 𝛑 * radius³ [11]
    • Again, to make things easier to measure, we ask you to include the full diameter and our calculator divides it by two to get the radius.

How Accurate Is The Aquarium Volume Calculator Overall?

If you choose your tank shape carefully from our aquarium volume calculators above you will be able to get a good volume estimate. You can increase the accuracy by including the weight of any objects in your tank.

But you should note that this is still an estimate. If you use this as a guide for any treatments for your tank ensure you follow the product manufacturer’s instructions carefully.

The Bottom Line

Home aquariums come in all shapes and sizes, so getting an accurate estimate for the volume of your aquarium can be tricky!

Whether you want to know the volume of your tank to work out the best maintenance schedule, or the dosage to medicate against fish diseases, hopefully, our calculators will help!

Photo of author
Andy Birks
Andy is the owner of Simply Aquarium and manages the team of experienced writers on the site. He loves helping fellow aquarists and introducing new people to the hobby!

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