Pool Filter Sizing

Looking for a new pool filter, but not sure what size will best fit your pool? There are a few items to keep in mind when deciding on your pool’s filtration needs.

1. Calculate Pool Volume

Before shopping for your favorite pool filter, it is important to understand how much water needs to be filtered (based on your pool volume).

Pool Supporter has made it easy with our Pool Volume Calculator article HERE. If you want to do the calculations yourself, here are a few easy formulas:

Square or Rectangle pool volume calculator: Length x Width x Depth x 7.5 = Volume (Gallons)

Square or Rectangle pool with variable depths: Length x Width x Average Depth x 7.5 = Volume (Gallons)

Round pool volume calculator: 3.14 x Radius Squared x Average Depth x 7.5 = Volume (Gallons)

Irregular pool volume calculator: 0.45 x (A+B) x Length x Average Depth x 7.5 = Volume (Gallons)

Oval pool volume calculator: ½ Length x ½ Width x 3.14 x Average Depth = Volume (Gallons)

2. Calculate Pool Capacity

Pool Capacity is defined as the number of gallons of water that a pool can hold. Pool Volume is the spatial measurement of a pool. Water is not filled all the way to the wall or deck line, which is why Pool Capacity is a lower number than Pool Volume.

Pool Capacity calculation: Pool Volume x 7.48 = Pool Capacity (Gallons)

3. What is the Flow Rate?

Flow Rate is defined as the volume of water flowing through a given point during a specific time frame, typically in gallons per minute (GPM) or per gallon (GPH). If you want to set up a pool filtration system that has an 8-hour turnover rate, you would need to calculate the flow rate to achieve that turnover rate/time. So, how is this done? Easy!

Flow Rate formula: Pool Capacity / Turnover Time (in hours) = Flow Rate.

Example calculation: 30,000 (gallon capacity pool) / 8 (hour turnover time) = 3,750 GPH Flow Rate.

4. What is the Filter Flow Rate?

Now, let’s determine if the pool filter you want can handle the flow rate requirement for your goal turnover rate. Filter Flow Rate is typically determined in GPM. Filter Area is the surface area of the filter medium (should be on the filter label/description).

Filter Flow Rate formula: Filter area x Filter Rate = Filter Flow Rate (GPM)

If researching this information seems daunting, both of the measures will be available from the filter manufacturer.

5. What Type of Pool Filter is Best?

The three main types of Pool Filters are: Sand, Cartridge and Diatomaceous Earth (D.E.). The most popular, and affordable, is the sand filter. The biggest difference between sand and other filters, is that sand filters don’t filter out as small debris as cartridge and D.E. filters. To learn more about the differences in pool filter options, check out our helpful article: Pool Filter Comparison Guide.

6. What’s the Right Size Pool Filter?

A good rule to remember is bigger, when it comes to Pool Filters, is better. Although larger filters are more expensive, they provide better filtering and easier maintenance for pool owners.

  • Increased time between cleaning and backwashing
  • Increased filtration of small particles
  • Increased longevity of filter media

7. Adjust the Filter Area and Rate

Pool Filter Rate may be regulated in certain locations. Maximum filter rates are set by the National Sanitation Foundation to ensure effective and efficient filtration. Filter Rate regulations are typically imposed with commercial pool installations, but you can compensate by selecting a filter with a larger filter area.

8. Choose Your New Pool Filter

Now it’s time to choose the perfect pool filter for you swimming pool. Take the previous calculations and information into account, you’ll find the best filter to keep your pool running strong.