Aquarium Volume Calculator
Work out how much water your tank holds. Useful before you calculate a water change, buy a heater, or follow a dosing instruction on a product label. Everything runs in your browser: nothing is sent anywhere and nothing is stored.
Enter your measurements and press Calculate.
How it is calculated
- Rectangular: length × depth × water height.
- Cylinder: π × (diameter ÷ 2)² × water height.
- Hexagon: for a regular hexagon measured flat-to-flat (width d), the floor area is (√3 ÷ 2) × d², about 0.866 × d². Multiply by water height.
- Bow-front: the rectangular volume plus an approximation of the curved bulge (about 2/3 × bow depth × length × height). Real tanks vary, so treat this as an estimate.
- Net volume: the gross figure minus the percentage you enter for substrate, rock and equipment. 10% is a rough starting guess for a lightly decorated tank; a heavily aquascaped reef can easily be 20–30%.
One US gallon = 3.785 liters. One liter of fresh water weighs about 1 kg (2.2 lb); salt water is a little heavier. Always check that your stand and floor can carry the filled tank.
Quick reference: common rectangular tanks
| Nominal size | Typical dimensions (L × D × H) | Approx. gross volume |
|---|---|---|
| 10 gal | 20 × 10 × 12 in | about 10 US gal / 39 L |
| 20 gal long | 30 × 12 × 12 in | about 19 US gal / 71 L |
| 29 gal | 30 × 12 × 18 in | about 28 US gal / 106 L |
| 55 gal | 48 × 13 × 21 in | about 57 US gal / 215 L |
| 75 gal | 48 × 18 × 21 in | about 79 US gal / 297 L |
Figures are approximations from the outer dimensions. Manufacturers differ and the water level sits below the rim, so measure your own tank.
This page is a general calculator, not advice about the care of any particular animal. Check your livestock's needs with a reliable specialist source.