Calculating Hexagon and Corner Tank Volume

Rectangular tanks are easy to measure, but many beautiful aquariums are not simple boxes. Hexagon, corner and bow-front tanks need their own formulas. This guide explains how to calculate the volume of these shapes so you can stock and dose them correctly.

Hexagon tank volume

A regular hexagon has six equal sides. The area of a regular hexagon is:

Area = (3 × √3 ÷ 2) × side²

To find the volume, multiply that area by the tank height, then convert to litres or gallons. Because the maths involves a square root, most aquarists prefer to let a calculator handle it.

Corner and quarter-cylinder tanks

Most corner tanks have a curved front and sit in the corner of a room. They are shaped like a quarter of a cylinder. To find the volume:

1. Calculate the full cylinder volume using π × radius² × height, where the radius is the curved face radius.
2. Divide the result by four.

A corner tank with a 40 cm radius and 50 cm height works out to π × 40² × 50 ÷ 4, which is about 62,832 cm³, or roughly 63 litres.

Bow-front tanks

A bow-front tank is a rectangular box with a gently curved front panel. Its volume is the volume of the box plus a thin curved segment along the front. The extra curve adds only a few percent, but the exact figure depends on how far the bow extends.

The easy way

Rather than working square roots and segments out by hand, open the fish tank volume calculator and select Hexagon, Corner bow front, Cylinder or Bow front. Enter your dimensions and the correct formula is applied automatically, giving you the volume in litres, US gallons and UK gallons.

A note on round fish bowls

Spherical fish bowls are sometimes sold as decorative tanks, but they are not recommended for keeping fish. They have a small surface area for gas exchange and are hard to filter. If you love a curved look, a cylinder or bow-front tank is a much healthier choice.