What Size Pool Pump Do I Need? GPM, Turnover and Filter Size

The flow a pool pump needs is the pool volume divided by the turnover time in minutes. A 20,000 gallon pool with an 8 hour turnover needs 42 gallons per minute (2,500 gallons an hour), through 1½ in pipe, and a filter of 2.8 ft² (sand), 111 ft² (cartridge) or 20.8 ft² (DE). The pool pump size calculator works out your pool.

Flow needed by pool size

Filter area for the flow

At an 8 hour turnover. Sand filters are rated at 15 GPM per ft² (up to 20 for high-rate), cartridge filters at 0.375 and DE at 2:

If you know the size, not the volume

For a rectangular pool, volume in gallons = length × width × average depth (feet) × 7.48. A pool 32 × 16 ft with an average depth of 5 ft holds 19,150 gallons and needs 39.9 GPM for an 8 hour turnover. The pool volume calculator handles round, oval and sloping pools.

Choosing the pump

• Match the flow to the head: the pump curve shows the flow it gives at each total dynamic head, so check it at your system's head (the resistance of the filter, heater, pipes and fittings, often 40 to 60 feet).
• Variable speed: these run slowly for many hours and save most of the electricity of a single-speed pump. Many areas now require them.
• Don't oversize: a pump that is too big wastes power, wears the filter and can exceed the safe water speed in the suction pipe.
• Suction safety: keep suction-side speed within the code, and use anti-entrapment drain covers.
• Check the filter can take at least the pump's flow.

See also the pool salt calculator. Estimates only: follow the pump and filter makers' guidance and your local code.

Frequently asked questions