Estimate litres per hour or gallons per hour from target turnover.
Open live calculator →A 180 litre aquarium at 5× turnover needs a nominal flow near 900 litres per hour.
Choose an hourly turnover target and calculate a starting rated flow for freshwater, planted or higher-flow aquarium planning.
The live tool updates immediately and shows the result in the units commonly used by aquarium keepers around the world.
Media, hoses and height reduce actual flow.
Match flow to livestock and aquascape.
Never assume a high rated flow replaces good maintenance.
Turnover is how many times per hour the filter moves the tank's whole volume. Common starting targets are 4–5× for a calm community tank, 6–8× for planted or messy setups with large fish, and 10× or more for reef systems where flow also feeds corals. These targets refer to the filter's real delivered flow, which is always lower than the number on the box.
Manufacturers rate pumps with no media, no hoses and no height difference. Add filter media, a metre of hose, an inline heater and the climb from a cabinet to the tank rim, and a canister rated 1000 L/h commonly delivers 500–700 L/h. That is why the practical rule is to buy a filter rated well above your calculated target—typically by 50–100%—rather than one that meets it exactly on paper.
A high number on the pump does not compensate for poor media or maintenance. Biological filtration depends on media surface area and mature bacteria; mechanical clarity depends on how often you rinse sponges. Meanwhile, some fish—bettas, fancy goldfish, many gouramis—actively dislike strong current. Match flow to the livestock and use spray bars or flow deflectors to spread it, rather than chasing the biggest number available.
At a general 5× turnover target you want about 1000 L/h of delivered flow. Because rated figures assume ideal conditions, a canister rated 1200–1500 L/h is a realistic choice for that tank.
Yes—species from still waters struggle in strong current, and very fast flow can blast substrate and stress plants. If fish fight the current constantly, diffuse the outlet with a spray bar or step the flow down.
The target range is similar, but sump returns lose noticeably more flow to plumbing height. Measure or estimate delivered flow at the tank, not the pump's rated figure, whichever filter type you run.