A common problem many pool owners face is that the cartridge filter in their pool is undersized. Undersized pool filters can be the cause of headache for pool owners because this will not only make the filter ineffective, but it will drastically shorten the life of the filter as well. A good rule of thumb when it comes to cartridge filter sizing is bigger is definitely bigger. Filter sizing is quite straightforward so we’ll keep this post short and sweet.

How do I know what cartridge filter size to select?

To determine the minimum cartridge filter size, you must first make sure that your pump is the right size for your pool.

Once you’ve ensured that your pump is the proper size, check the table below for the surface area of the cartridge filter needed for the MAXIMUM or OPTIMAL flow rate of your pump.

Filter Surface Area Pump Maximum Flow Rate Pump Optimal Flow Rate

100 sq feet

38 GPM

30 GPM

200 sq feet

75 GPM

50 GPM

300 sq feet

112 GPM

75 GPM

400 sq feet

150 GPM

100 GPM

500 sq feet

150 GPM

125 GPM

Alternate Way of Determining Cartridge Filter Size

Another thing to consider is the volume of your pool water. While this isn’t scientific, we recommend a filter surface area of 100 square feet for every 35,000 liters of water volume for your pool.

Already have a cartridge filter?

If your filter is already correctly sized and you just need a replacement filter, we have written a comprehensive guide on how to measure your filter for replacement, just click on the button below.


Cartridge Filter Sizing is pretty straightforward. It’s okay to get a bigger one (less maintenance and cleaning on your part) but NEVER get an undersized one. While you can get away with the exact filter size with no problems, getting the biggest one that your budget allows will save you from a lot of cleaning and maintenance tasks, not to mention that they will last longer as well.

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