The method
How aquarium volume is calculated
Every shape on this site follows one rule: find the floor area, multiply by the height, then convert the cubic result into gallons or litres. For a rectangular tank the floor is simply length × width. In inches, dividing the cubic total by 231 gives US gallons; in centimetres, dividing by 1,000 gives litres.
Shape changes only the floor-area step. A cylinder uses π × r², a hexagon 2.598 × s², a bow front adds a half-ellipse to a rectangle. Pick the wrong one and the error is rarely small: treating a bow front as a box or a hexagon as a cube is a 10 to 30 percent mistake, which flows straight into medication doses, filter turnover and stocking decisions.
The second rule is to measure inside the glass. Exterior sizes include panel thickness and trim, and larger tanks use thicker glass. The glass thickness table shows how much that costs. Finally, nobody fills a tank to the rim, and substrate and rock take up space below the water line. Every calculator here lets you enter the real water height and a substrate depth, and the displacement tool handles hardscape and equipment.
See every formula