how to calculate pool filter size


Author: Poolking - Swimming Pool Equipment Manufacturer

As a pool owner, it's crucial to ensure that your swimming pool stays clean and clear. One of the most important components of a pool is the filter, and it's essential to choose the right size filter to keep your pool healthy. In this guide, we'll show you how to calculate pool filter size to make sure you're optimizing your pool's filtration system.

Understand Pool Filtration Basics

Before we dive into pool filter sizing, it's important to understand the basics of pool filtration. The filtration system's job is to remove dirt, debris, and other contaminants from the pool water. During this process, water circulates through the pool's intake and skimmer, through the filtration system, and back into the pool.

There are three types of pool filters: sand, cartridge, and DE (diatomaceous earth). Each has different pros and cons, and the filter size calculation method we'll be discussing applies to all three types.

Step One: Determine Your Pool's Gallons

The first step in calculating the right filter size for your pool is to determine your pool's volume. You need to know the number of gallons of water that your pool holds. This calculation is necessary to ensure that your filter can handle the amount of water in your pool.

You can find the pool's volume by calculating the length, width, and depth of your pool. Once you have these dimensions, use the following formula:

Length x Width x Average Depth x 7.5 = Total gallons

Step Two: Calculate the Turnover Rate

The turnover rate represents the number of hours it takes for your pool's water to circulate through the filtration system entirely. Pool experts recommend turning over the pool's water once every day.

To calculate the turnover rate, divide your pool's total gallons by the flow rate (GPM) of your filter. This calculation will give you the number of hours it takes your filter to handle the entire pool volume.

Total gallons / GPM = Turnover rate (in hours)

Step Three: Determine Your Filter Size

Now that you know your pool's turnover rate, it's time to determine the correct filter size. The filter size calculation should be the maximum GPM your system needs to handle your pool size.

To calculate it, you multiply the turnover rate by the pool's volume, then divide that number by the desired operating hours (typically 12 to 24 hours per day). The final result will give you the maximum GPM or flow rate that your filter needs to achieve.

Total gallons x Turnover rate / Operating hours = Required GPM

Once you have the required GPM, you can choose the appropriate filter size that can handle it. Pool filter manufacturers usually provide a product chart, so you can select the right filter for your calculated GPM.


Pool filter sizing is an essential aspect of keeping your pool clean and healthy for swimming. An undersized filter will not be able to keep up with your pool's turnover rate, while an oversized filter can waste energy and cost more money.

Calculating your pool filter size is a straightforward process that requires knowledge of your pool's volume, turnover rate, and required GPM. With this information, you can make the best choice for your pool and ensure that it stays sparkling and safe for swimming.


Just tell us your requirements, we can do more than you can imagine.
Send your inquiry

Send your inquiry

Choose a different language
Current language:English