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Aquarium Volume Calculator

Calculate volume for different aquarium shapes – rectangular, round/cylinder or bow-front

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🇩🇰 All calculations are based on Danish rules, rates, and currency (DKK). This calculator is translated for convenience but applies exclusively to Denmark.

Calculate volume for your aquarium

Not all aquariums are rectangular. This calculator handles three different shapes: rectangular, round/cylindrical and bow-front. The correct volume is crucial for dosing medication, calculating fish numbers and water care.

Rectangular aquarium

The most common shape. Volume is simply calculated as length x width x height / 1000 to get litres. A standard 80x35x40 cm aquarium holds about 112 litres gross.

Round or cylindrical aquarium

For round or cylindrical aquariums the formula is pi x radius squared x height / 1000. Enter the diameter as the first measurement – the calculator finds the radius. Cylindrical aquariums have less surface area relative to volume, which can affect oxygen exchange.

Bow-front aquarium

Bow-front aquariums have a curved front that gives more volume than a rectangular aquarium with the same base measurements. We approximate the volume as 85% of the corresponding rectangular volume, as the bow typically adds extra depth in the middle.

Net vs. gross volume

Net volume is about 90% of gross volume, as gravel, decorations, filter and heater displace water. Use net volume for dosing medication and water treatment products for correct concentration.

Frequently Asked Questions

Which aquarium shape is best?

Rectangular aquariums are generally best for fish as they provide the most surface area for oxygen exchange and most swimming space. Bow-front aquariums give a nice visual effect and slightly more volume. Cylindrical aquariums can be attractive but offer less horizontal swimming room. Avoid very tall, narrow aquariums – fish prefer length over height.

How do I calculate volume for a hexagonal aquarium?

For a hexagonal aquarium you can use the cylinder formula as a good approximation since a hexagon resembles a circle. Measure the distance between two opposite sides (width) and use that as diameter. The result will be about 10% too high, but this is partly compensated by net volume being about 90% of gross.

Does the aquarium shape affect how many fish I can have?

Yes, shape affects both surface area (oxygen exchange) and swimming space. A wide, shallow aquarium with large surface area can hold more fish than a narrow, tall aquarium of the same volume. Surface area is often the limiting factor – not volume alone. Territorial fish also need horizontal space.

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