Fish tank water and operating-weight tool
Aquarium Volume Calculator
Calculate aquarium water volume in US gallons, UK gallons and liters, then estimate water weight and total operating weight after displacement and connected-system volume.
Aquarium volume formulas
rectangular volume = internal length × internal width × actual water depth
cylindrical volume = π × internal diameter² ÷ 4 × actual water depth
regular-hexagon footprint = √3 ÷ 2 × distance across flats²
display water = gross volume × (1 − displacement percentage)
system water = display water + connected sump or reservoir water
The calculator uses exact conversions of 1 in³ = 0.016387064 L, 1 US gal = 3.785411784 L and 1 UK gal = 4.54609 L. Water weight uses the density you enter.
Checked example
| Input | Value |
|---|---|
| Display tank | 48 × 18 in footprint, 20 in water depth |
| Displacement and sump | 10% displacement; 10 US gal connected water |
| Density and dry weight | 1.025 kg/L; 200 lb dry system |
The gross display volume is 74.81 US gal. After 10% displacement the display holds about 67.32 US gal; adding 10 US gal gives 77.32 US gal or 292.71 L. Water weighs about 661.4 lb, and the estimated operating weight is 861.4 lb.
Limits and safe use
- Use inside dimensions and actual water depth. Outside glass or acrylic dimensions overstate water volume.
- Displacement is an estimate. Measuring water added during filling is more reliable for treatment dosing.
- The connected-volume input must represent operating water, not the sump’s empty geometric capacity.
- Dry weight should include the tank, stand, canopy, substrate, rock, equipment and other supported items.
- Do not use total weight alone to approve a floor, cabinet, stand, glass thickness or acrylic thickness; load distribution and structural details matter.