Aquarium volume calculator (any shape)
Work out how many gallons or liters your tank holds: rectangle, bow-front, cylinder, half-cylinder, corner or hexagon. Formulas shown.
How the volume is calculated
Water volume is the area of the tank’s footprint times the water height. Use inside dimensions if you can; outside measurements include the glass and slightly overstate volume. Subtracting the gap between the water line and the rim gives a more realistic figure than the “nominal” size printed on the box.
| Shape | Footprint area |
|---|---|
| Rectangle | L × W |
| Cylinder | π × (D/2)² |
| Half-cylinder | ½ × π × (W/2)² |
| Corner (quarter-cylinder) | ¼ × π × S² |
| Regular hexagon | (3√3 ⁄ 2) × S², where S is one side |
| Bow-front | L × W plus a circular segment with chord L and depth B. The arc radius is R = (L²/4 + B²) ÷ (2B), the angle is θ = 2·asin(L ÷ 2R), and the segment area is R²/2 × (θ − sin θ). |
Unit conversion: 1 US gallon = 231 cubic inches = 3.785411784 liters exactly; 1 Imperial gallon = 4.54609 liters; 1 liter = 1,000 cm³.
Worked example
A 30 × 12 × 18 inch rectangular tank filled to 1 inch below the rim holds 30 × 12 × 17 = 6,120 in³. Divided by 231, that’s 26.5 US gallons (100.3 L). Real water volume is lower again once gravel, rock and equipment are added.
Sources
Related tools: Gallons ↔ liters & water weight · Water change & nitrate dilution · Substrate / gravel amount · Heater size & warm-up time · Product dose scaling