Calculate the operating water volume inside a rectangular sump.
Open live calculator →A 60 × 35 cm sump running at 25 cm holds about 52.5 litres before displacement.
Estimated operating water after the selected displacement.
Use the internal sump footprint and normal operating water height to estimate litres and gallons available in the filtration system.
The live tool updates immediately and shows the result in the units commonly used by aquarium keepers around the world.
Use internal dimensions.
Subtract media and equipment displacement.
Leave enough empty capacity for drain-down when the return pump stops.
Bigger is almost always better—common practice is a sump around 20–30% of display volume, sized mostly by what fits the cabinet. More volume stabilises temperature and chemistry.
A sump never runs full: it needs empty capacity to swallow drain-down when pumps stop. Operating volume—the level during normal running—is what counts toward system water volume.
Yes, sump water adds real dilution and stability to the system, though swimming space in the display still limits what fish you can keep.