A cylinder aquarium has a circular base, so its volume comes from the diameter and the height. The diameter is the distance across the circle through its centre, measured on the outside — not the radius.
The curved glass makes measuring awkward. The most reliable method is to hold two rulers or flat boards against the widest point and read the distance between them.
How is the volume of a cylinder aquarium calculated?
Gross volume (litres) = π × (diameter ÷ 2)² × height ÷ 1000. Divide cubic inches by 231 for US gallons. For the net water volume, two glass thicknesses are subtracted from the diameter, and the bottom glass, substrate and headroom from the height.
How to take the measurements
- Measure the diameter at the widest point on the outside.
- Measure the height from the bottom to the top rim.
- Measure the glass thickness at the top rim.
- Enter the substrate height and headroom in the advanced settings.
Worked example
For a cylinder aquarium with diameter 50 cm, height 60 cm, the gross volume is 117.8 litres. With 0.8 cm glass, no substrate and 2 cm of headroom, the net water volume is 105.2 litres.
Example sizes and their volumes
| Diameter (cm) | Height (cm) | Gross (L) | Net water (L) | Net water (US gal) |
|---|---|---|---|---|
| 30 | 40 | 28.3 | 23.6 | 6.2 |
| 40 | 50 | 62.8 | 54.7 | 14.4 |
| 60 | 60 | 169.6 | 153.2 | 40.5 |
| 100 | 50 | 392.7 | 358.9 | 94.8 |
Net water volume assumes 0.8 cm glass, 0 cm substrate and 2 cm headroom; results are approximate.
Frequently asked questions
Should I enter the diameter or the radius?
Enter the diameter. The calculator works out the radius itself; entering the radius would give a result four times too small.
How many litres is a cylinder tank 50 cm across and 60 cm tall?
π × 25² × 60 ÷ 1000 ≈ 117.8 litres gross.
How does a cylinder compare with a box of the same size?
A cylinder whose diameter and height equal the side and height of a box tank holds π/4 of its volume, about 78.5%.