Your swimming pool pump helps circulate water so it does not stagnate and will move through the pool's filter. The size of a swimming pool pump is measured by how much water it can pump per minute. The size is determined by your pool volume, how often you want your pool water to turn over and the size of your intake values.

Minimum Pump Size

Calculate the size of your pool in gallons. The formula for rectangular pools is length times width times average depth times 7.5. The formula for circular pools is the radius squared times the average depth times 5.9. The formula for oval pools is the long diameter times the short diameter times the average depth times 5.9. You also need to determine how often you want your pool to turn over. Most pools are completely filtered every eight to 12 hours. The more use your pool gets, the more often you will want it to turn over. Because pool pumps are measured in gallons per minute, multiply the time by 60 to convert it to minutes. To determine the minimum flow rate you need for your pool, divide the volume by the turnover time. For example, a 27,000-gallon pool that turns over every 10 hours would need a unit capable of pumping 45 gallons per minute.

Maximum Pump Size

To determine the maximum size for your pool pump, you need to know how much water your intake lines are capable of handling and how much your filter can handle. The amounts are dependent on their size. For example, a 1.5-inch pipe generally can handle about 43 gallons per minute, a 2-inch line about 73 gallons and a 2.5-inch pipe about 120 gallons. The size of your filter can be calculated by multiplying its surface area by the filter rate, which depends on the type of filter you have. For example, a 5-square-foot sand filter with a filter rate of 15 gallons per square foot has a maximum flow rate of 75 gallons per minute. The maximum flow rate is the the lesser of the two numbers.

Choosing a Pump

If you have only a pool, consider getting a pump closer to the minimum size needed. However, if you have a pool and spa combination, you should get a pump closer to the high end of your range.

Source:

Pool Pump Size

How to Measure Pool Volume