Hexagon vs Flat Back Hexagon Aquarium Volume
Quick Answer
A full hexagon aquarium has six equal sides and sits freestanding. A flat back hexagon has one flat side that rests against a wall. They use different volume formulas and different calculators.
Shape Differences
A regular hexagonal aquarium has six equal-length glass panels forming a symmetric hexagon when viewed from above. It is a freestanding design viewable from all sides. A flat back hexagon aquarium replaces the rear panel arrangement with a single long flat panel designed to sit flush against a wall. In this calculator's outline that makes six panels in all: a flat back, two straight side panels, two angled front-corner panels and a flat front panel, with five of them visible from the room. The back is the widest panel, so the outline is a rectangle with its two front corners cut away, not a hexagon with equal sides.
Measurement Differences
A regular hexagon requires only one side length measurement (all six sides are equal) plus the height. A flat back hexagon requires five measurements: the back length, the overall depth, the front panel width, the straight side panel length and the height. The flat back version needs more measurements because its panels are not all equal length. See our guide on measuring your tank accurately for the full procedure.
Formula Differences
The regular hexagon uses the formula V = (3√3 ÷ 2) × s² × H, where s is the side length. The flat back hexagon uses V = (L × W - (L - F) × (W - P) ÷ 2) × H, the rectangle of back length by overall depth less the two cut front corners, where F is the front panel width and P is the straight side panel length. Using the wrong formula will produce incorrect results because the cross-sectional areas are different.
Which Calculator Should You Use?
Count the panels and check the back of the tank. If your tank has six equal panels and no flat back wall, use the hexagon calculator. If your tank has one wide flat back panel designed for wall placement, use the flat back hexagon calculator.
Example Comparison
A regular hexagon with 8-inch sides and 20-inch height: V = (3√3 ÷ 2) × 64 × 20 = 3,326 cubic inches = 14.40 gallons. A flat back hexagon with a 36-inch back length, 12-inch overall depth, 24-inch front panel width, 6-inch straight side panel length and 16-inch height holds 6,336 cubic inches = 27.43 gallons. Entering its 24-inch front panel as the side length in the regular hexagon formula would give 103.65 gallons, about 3.8 times too much, so the two shapes are not interchangeable for volume calculations. To translate any gallon result to litres, use the unit converter.