Because both straight sides equal the radius, you only need one wall measurement and the height. The result is exactly one quarter of a full cylinder with that radius.
How to measure a corner cylinder tank
- Measure the inside length of either straight wall side. Both should match; if not, you likely have a corner bow front or corner prism.
- Do not measure the curved front: it is longer than the radius and will overstate volume.
- Height is measured on a straight panel.
Always measure inside the glass. Exterior sizes include the panel thickness and any trim, which on larger tanks can remove 5 to 10 percent of the apparent volume. See the measuring guide for the full method.
Corner Cylinder volume formula
V = π × r² × H ÷ 4
A quarter of a full cylinder. The two straight sides that meet in the corner are both equal to the radius.
With inches, divide the cubic result by 231 to get US gallons and multiply gallons by 3.785 for litres. With centimetres, divide by 1,000 for litres directly.
Worked example
Inputs: Radius 24 inHeight 24 in
π × 24² × 24 ÷ 4 = 10,857 in³, which is 47.0 US gallons or 177.9 litres.
A quarter of a cylinder, three quarters of the view
Corner cylinders use the least floor space of any curved tank for a given radius, yet the entire front is a viewing panel. Their volume is 78.5% of a square corner tank with the same wall length, so if you are choosing between a quarter cylinder and a square corner cube, expect to give up about a fifth of the water for the curve.
Getting to real water volume
The formula gives the geometric volume of the tank to the rim. Three things make the real water volume smaller, and the calculator above lets you account for two of them directly:
- Fill height. Most tanks run an inch or two below the rim. Enter the actual water line and the result scales to match.
- Substrate. Gravel and sand sit in the water column. The substrate option removes the solid fraction of the bed (62 percent of its depth for typical gravel) from the total.
- Rock, wood and equipment. Use the displacement calculator to subtract hardscape by weight and equipment by type.
Water weight
Fresh water weighs about 8.34 pounds per US gallon (1 kg per litre). Reef water at a specific gravity of 1.025 is about 8.55 pounds per gallon. The calculator shows both so you can check what your stand and floor will carry before adding glass, substrate and rock on top.