The first job of the pool pump is to circulate the pool water through the filter and back out to the pool. To do so, the pump must have a minimum flow rate in GPM (gallons per minute) that will allow it to move all the water through the filter within a given amount of time.

To determine the minimum flow rate you must do two things:

Determine the capacity of your pool in gallons.

Rectangular Pools – Length x Width x Average Depth x 7.5 = Gallons in Pool

If the pool is 30 feet long by 18 feet wide by 4.5 feet deep, the approximate pool volume is 18,225 gallons.

(30 times 18 times 4.5 times 7.5)

Round Pools – Radius x Radius x 3.14 x Average Depth x 7.5 = Gallons in Pool

If the round pool has a 14 foot radius, and a depth of 4.5 ft. then the approximate pool volume would be 20.771

(14 times 14 times 3.14 times 4.5 times 7.5)  REMEMBER: Radius equals diameter divided by 2.

Determine the desired turnover rate.

In other words, how long should it take to move the entire contents of your swimming pool through the filter.  Divide the pool gallonage by the turnover rate to determine the minimum flow rate per hour.  Divide that number by 60 to determine the minimum flow rate per minute.

If the pool holds 20,000 gallons of water and enjoys a medium level of usage, you would look at the 20,000 gallon line and go to the 8 hour turnover column (for medium use).  You would find that the pool requires a 41.7 gallon per minute flow rate to achieve proper turnover.  You can look at the pump charts to find out the pump that will deliver that level of performance.

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