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How to Size a Pool Filter and Pump System

How to Size a Pool Filter and Pump System. Your swimming pool is a big investment, so you want it to run smoothly for years to come. Choosing the correct size pump and filter system will ensure that your water is well-filtered and that the pipes won't be damaged by excessive water pressure. It will also ensure that your pool is as energy-efficient as possible.

Measure Your Pool

Measure your pool's width, length and depth. Write the measurements down in feet, using decimals to approximate fractions of feet. (In other words, 20 feet, 3 inches would be 20.25 feet.)

Multiply the length of your pool by its width to determine its surface area.

Multiply the pool's surface area by its depth, and the product of that operation by 7.9 to determine how many gallons of water your pool holds. This formula will work only if your pool is perfectly rectangular. For other pool shapes, visit's pool volume calculator page (see Resources below).

Choose a Pool Pump

Divide the number of gallons of water your pool holds by 8. Then, divide the quotient by 60. This will determine the minimum flow rate you need use to ensure the water in your pool can make a complete circulation every 8 hours.

Determine the maximum flow rate your pool can handle by looking at its plumbing system. Most pools use 2-inch pipes, which can handle about 73 gallons per minute. A 1.5-inch pipe can handle less than 45 gallons per minute, while a 3-inch pipe can handle more than 150 gallons per minute. Use a slightly lower flow rate if your plumbing has a lot of intricate turns and connections that could be stressed by too much rushing water.

Select a pool pump with a flow rate between your minimum and maximum allowance.

Consult a professional for complicated systems that involve using a single pump for multiple pools, or multiple pumps for a single pool.

Choose a Pool Filter

Determine the optimal flow rate your pool's filter system needs to achieve maximum efficiency. Use your pool's surface area, then refer to the computation chart provided by (see Resources below).

Make sure your filter's maximum flow rate, specified by the manufacturer, will accommodate the size of your pump.

Choose a filter of a larger size if you want the cleanest water with the lowest amount of maintenance. You will need to clean the filter when it becomes clogged with debris. A larger filter will take longer to clog.


When measuring depth, use the depth of the actual water level, not the full depth of your pool. Many pool professionals recommend a pool turnover rate of 8 hours, but this is a ballpark figure and it's fully adjustable. There are 3 types of filters: Diatomaceous Earth (D.E. filters), sand filters and cartridge filters. D.E. filters will get your water the cleanest, but often they are the most expensive. Cartridge filters are easiest to maintain, but you must buy a new filter each year. Sand filters are the cheapest, but the water they filter will not be as clean.

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