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Fish Tank Volume Calculator

Octagon Fish Tank Volume Calculator

Volume

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Enter your tank dimensions to see the volume.

Did we solve your problem?

Calculate the volume of an octagonal aquarium. Enter the side length and height and get the capacity in litres and gallons.

How octagon tank volume works

A regular octagon has eight equal sides. Its area is 2 times (1 plus the square root of 2) times the side squared. Multiply that by the height for the volume, which the calculator handles for you.

Shape preview

Adjust the size and height to see this tank shape and its volume.

Volume ≈ — litres

How to calculate fish tank volume

Measure the length, width and height of your tank, then multiply them together. Change the values below and the diagram and the calculation update instantly.

  1. 1

    Measure length, width and height

    60 x 30 x 30 cm

  2. 2

    Multiply them for cubic centimetres

    60 x 30 x 30 = 54,000 cm³

  3. 3

    Convert to litres and gallons

    54,000 ÷ 1000 = 54 litres (14.27 US gal)

Formulas behind the fish tank volume calculator

Prefer to calculate the aquarium size by hand? Here is the volume formula for each tank shape. Click a card to try it in the calculator.

For unusual tanks, see a triangular prism volume tool, and note that spherical aquariums (fish bowls) are not recommended for keeping fish.

Aquarium shapes

Our fish tank volume calculator supports seven popular aquarium shapes. Click any shape to load it into the calculator above.

Frequently asked questions

How do I calculate octagon fish tank volume?
Enter the side length and the height. The calculator uses the regular octagon area times height.
What is the side length of an octagon tank?
It is the length of one of the eight equal straight edges, measured on the inside.
How do I get octagon volume in gallons?
Find the volume, then switch the result unit to US or UK gallons.
Are octagon tanks practical?
They make striking display tanks, though their many panels can make custom builds more expensive.
What units can I use in this calculator?
You can switch between centimetres, millimetres, inches, feet and metres at any time. Enter all dimensions in the same unit and the result updates instantly.
Does the result include substrate and decoration?
The figure is the full internal capacity. Subtract roughly 10 to 15 percent for substrate, rocks and the gap you leave at the top to estimate the real water volume.
How accurate is this fish tank calculator?
It uses the exact geometric formula for each shape, so the result is accurate for the dimensions you enter. Measure the inside of the tank for the best accuracy.
Is this calculator free to use?
Yes. It is completely free, needs no sign-up, and works on phones, tablets and desktops.

Calculator tools

Explore our specialised fish tank volume calculators, each tailored for a specific unit, shape or region.

In Gallons In Litres Tank Size Capacity Dimensions Water Volume Tank Weight In CM In MM In Inches In Feet Metric Hexagon Corner Cylinder & Round Bow-front Triangle Octagon Pentagon Surface Area UK Australia

Related guides

Learn the core ideas behind fish tank volume before or after using the calculator.