Pool pump turnover and flow rate calculator

A "turnover" is the time it takes the pump to move a volume of water equal to the whole pool. Enter your pool's volume and a turnover time to get the flow rate you need, or enter your pump's flow to see how long one turnover takes.

The formulas

How long should the turnover be?

For residential pools, a turnover of around 6–8 hours is a common design target, and many owners aim for at least one full turnover a day. Public pools must meet the turnover times in their local health code, which are often shorter. One turnover doesn't filter every drop: because filtered water mixes back in, one turnover passes roughly 63% of the water through the filter, and two pass about 86%. Clear water depends on good chlorine and pH more than on long run times.

Worked example

A 15,000-gallon pool with an 8-hour turnover: 15,000 ÷ (8 × 60) ≈ 31 GPM. A pump that actually delivers 50 GPM turns the pool over in 15,000 ÷ (50 × 60) = 5 hours.

Why your pump's label isn't its real flow

A pump's flow depends on the resistance of the plumbing, filter and equipment it pushes against, called total dynamic head and measured in feet. The flow printed on a box is usually at a low head. Real systems often run at 40–60 feet of head or more, where the same pump delivers much less. To know your real flow, read it off the manufacturer's pump curve at your system's head, or install a flow meter.

Variable-speed pumps

Variable-speed pumps save energy by running slowly for longer. The physics favors slow running: halving the speed roughly halves the flow but cuts power use to about an eighth. So running at half speed for twice as long moves the same water for roughly a quarter of the energy. Use higher speeds only when you need them, for example for a heater, a salt cell's minimum flow, suction cleaners, water features or vacuuming. Check each piece of equipment's minimum flow requirement.

Frequently asked questions

How many hours a day should I run my pool pump?

Long enough for at least one turnover a day, and longer in hot weather, during heavy use or while clearing algae. Saltwater pools need enough run time for the cell to make the day's chlorine, which may be longer than the turnover.

Is a bigger pump better?

Not necessarily. Too much flow can exceed the filter's rated flow, reduce filtering and raise energy bills. Match the pump to the filter, the plumbing size and any equipment's flow limits.

What about the filter size?

Every filter has a maximum flow rate on its label. Keep the pump's real flow under it. A larger filter usually means longer gaps between cleanings.