How To Size a Pool Filter

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Before you can select the correct filter for your pool, you must first select the correct pump for your pool. Your pool filter must be matched to your pool pump. If the filter is too small relative to the pump. the pump will generate more water pressure in the filter than the filter is able to handle. This imbalance will quickly break down the filtering material of the filter which will greatly diminish the effectiveness of the filter. In more extreme cases, the high-pressure build-up may cause cracks in the filter tank causing it to explode. This guide covers how you should size your pool filter correctly.

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Related Article: How to Size an Above Ground Pool Filter 

Step by Step

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Step 1

SIZE POOL - A standard pool circulation rule is to be able to filter all that water in your pool at least once a day. Customers generally run their single speed pump for an 8 hour period, so they require a pump/filter system that will recycle their pool water in an 8 hr period. The first step then is to calculate the total gallons in your pool. See our guide on "How to Size a Pool Pump for Your In-Ground Pool" for the formulas required to size your pool. For this guide, we will assume a typical in-ground pool size of 20,000 gallons.




Step 2

DETERMINE GPM REQUIRED - After you have the number of gallons in your pool (20,000 gallons for this example), you will have to calculate the Gallons Per Minute (GPM) required to filter 20,000 gallons in 8 hours. To come up with this flow rate first divide your calculated gallons by 8 for Gallons Per Hour (GPH). Then divide that number by 60 to get Gallons Per Minute (GPM). For our example of 20,000 gallons that's: 20,000 / 8 hours or 2,500 GPH divided by 60 mins/hour or 42 GPM.

Step 3

DETERMINE Feet of Head - As water flows through the system piping between the pool and the pump, it will meet with resistance to flow according to factors like the length of the piping, number of turns (elbows) and the diameter of the piping. This resistance is called "Feet of Head or "Head". As Head increases, your pools actual GPM will decrease. Calculation of Head can be involved and is generally done during the initial installation of the pool. However for a rough estimated use the average of the lengths of the suction lines between the pool and the pump. Most basic in-ground pools have a head of 40 to 50'.We will assume 45' for this example.

Step 4

DETERMINE PUMP SIZE - Now that you have determined your pools required GPM and its Feet of Head, you have the information required to select your pool.'s pump size. Go to the description page of the style of pump you would like to purchase. Many pump manufacturers will provide a chart on this description page showing the HP required for your particular GPM and Foot of Head requirement. For example, say you wanted the popular Hayward Super Pump. An abbreviated version of the Hayward Super Pump Performance Page is shown at the left. Based on the data above, we are looking for a pump that will handle 42 GPM with a 45 Feet of Head. According to the chart for 50 Feet of Head (closest above to 45'), we need a pump between 3/4 HP (31 GPM) and 1 HP (50 GPM). Since we always go to the higher GPM, we would select the 1 HP pump.

Step 5

DETERMINE FILTER SIZE - The size of your pool filter is directly related to the pool pump you have selected. If your pool filter is too small for the pump, there will be additional strain on the pump motor as it tries to push water through and meets resistance at the filter. This will eventually burn out the pump motor and your filtration will also be compromised. We recommend over-sizing the filter to be absolutely certain it can handle the flow coming from the pump. So in this case, instead of getting a filter rated at exactly 42 GPM, you should select one that is a little higher – around 60 GPM would be fine.

Click Here to View Available Pool Filters

Step 6

OTHER CONSIDERATIONS - There are a couple of other considerations that should be mentioned in your selection of a pool pump and filter. The above calculations are based on a basic pool configuration with no extra water features: fountains, spas, waterfalls, solar heating, and in floor cleaning systems. The features generally require higher GPM rates which equates to a higher HP pumps/filters. Also if your pool requires greater than 60 GPM you may need at least 2" diameter suction pipes. Suction pipes of 1 1/2" have a physical limit of 60 GPM. 2" pipes can handle up to 100 GPM.

Step 7

DETERMINE AG POOL FILTER SIZE - The size of your system is mostly determined on the size of your above ground pool. The gallons found inside your pool will give you the horse power needed for your pump. A simple rule to follow is you should be able to clear all of the gallons of your pool in an 8 hour period of time. You can use the following as a guideline.

• Above Ground Pool up to 24 Ft. Round = 1 HP pump
• Above Ground Pool over 24 Ft. Round = 1 ½ HP pump

Comments

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(1 to 40 of 166)

Anonymous  Posted: 6/12/2021 

I have Haywood 1100 filter need new filter should I get Haywood 1200 or newvswimclear Haywood sizec100s orc1505s
 Reply

InyoPools Product Specialist  Posted: 6/17/2021 

Ether would work. I always suggest going with the same size or bigger when replacing a filter to prevent any pressure issues. Plus, if you go bigger, you may go longer between cleanings.
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Anonymous  Posted: 6/2/2021 

I have a 21 ft round above ground pool, 52inches deep. I bought a 1.5 horsepower pump. What size sand filter should I have?
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InyoPools Product Specialist  Posted: 6/4/2021 

At least an 18" tank sand filter would be needed for that 1.5 HP pump. For example, the Sand Filter with Top Mount Valve 18" Tank - W3S180T would work pretty well with a 1.5 HP pump.
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 Posted: 5/17/2021 

Would a 24 inch, 300 lb sand filter work for a 24,000 gallon pool?
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InyoPools Product Specialist  Posted: 5/21/2021 

As mentioned in the guide, the size of the pump also plays a part in the size of the filter. What is the model number of your pump?
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 Posted: 5/15/2021 

The tank on my 20 year old Purex Triton Nautilus FNS DE filter burst. I need to replace the filter system. The existing filter has pipes at 9 1/2 and 17 inches above the concrete pad. New systems that I have seen have pipes at 8 and 15 1/2 inches. Can I put pressure treated boards under the new filter to raise it 1 1./2 inches? Or what would be my solution?
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InyoPools Product Specialist  Posted: 6/4/2021 

I'd prefer a cement block over wood paneling just for the longevity of the material.
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 Posted: 5/3/2021 

Have in ground pool approximately 7200gal have older model pentair de filter with 1hp motor. Would like to get a cartridge filter. What size filter should I get.
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InyoPools Product Specialist  Posted: 5/13/2021 

A pool that size could use the Clean & Clear 75 sq/ft Cartridge Filter - 160315.
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 Posted: 4/29/2021 

I have a 24,000 gallon in ground pool with 2" plumbing. There's a water feature w/1.5" plumbing that we only use occasionally. All of my equipment is old and starting to have issues. Would like to replace the DE filter with a cartridge type. Need help sizing the pump, motor, and filter.
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InyoPools Product Specialist  Posted: 5/14/2021 

Please provide model numbers of the equipment you are replacing. This is the easiest way for me to figure out what type of equipment should replace it.
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 Posted: 4/13/2021 

Looking for the correct size filter for an 18000 gal pool, with a 1.5 hp pump.
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InyoPools Product Specialist  Posted: 4/16/2021 

First, is this an inground or above ground pool? Second, what type of filter are you looking for? Sand, Cartridge, or DE
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 Posted: 3/3/2021 

I have an 18ft round pool 48 deep. What size pump and sand filter do I need?
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InyoPools Product Specialist  Posted: 3/4/2021 

This article is mainly for inground pool systems. Is your 18' round pool an above ground model? If so, this guide would be more helpful to you: How To Size an Above Ground Pool Pump and Filter System.For an above ground pool of your size, you would need a 1 HP pump, and at least a 16-inch tank sand filter. For example, this would be a suitable system for your pool: Carefree 16" Sand Filter w/ Hi-Flo II 1.0 HP Pump - 520-5307-6S
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 Posted: 3/2/2021 

I have a 15,000 gallon inground pool with a 1.65hp motor. I want to change out my old StaRite filter system with a newer Hayward Filter Cartridge. Not sure which size sq ft would be best and the Hayward model number recommended. Thanks
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InyoPools Product Specialist  Posted: 3/4/2021 

A big help with this would be to know what is the model number of your current filter. This would let us know what your current filter's square footage is, giving us a jumping-off point. Do you know the model number or cartridge number of your filter?
 Reply

 Posted: 2/7/2021 

I have a 11,000 in ground pool serviced with a 2hp pump and a Hayward S-244S sand filter now. Pipe size is 2.5" I would like to replace it with a cartridge filter. Can you recommend a filter?
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InyoPools Product Specialist  Posted: 2/8/2021 

For a pool that size I would go with the Waterway ProClean Plus 125 Sq. Ft.. The filter has the flow rate capacity to keep up with your pump and the and it is large enough so that you do not need to clean too often. Of course, you can always go up a size or two. Do this will allow you to go even longer between cleanings.
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 Posted: 11/12/2020 

I have a 16000 gallon inground pool with an old DE filter that needs replaced. I am thinking of going to a cartridge filter. My pump is a 1HP uprated to 1.25 and I would like to know what size cartridge filter I need. Would a 150 square foot do the job for me?
 Reply

InyoPools Product Specialist  Posted: 11/16/2020 

Yes, a 150 square foot filter like the ProClean Plus 150 sqft Pool Cartridge Filter - PCCF-150 or the Clean & Clear Cartridge Filter 150 sqft would be great for your setup. That size provides an outstanding balance of flowrate and filtering capacity, which should make maintenance easier.
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 Posted: 10/14/2020 

Have to replace my Hayward Perflex Extended Cycle D.E. Filter, can it be replaced with a Hayward W3C1200 Swim Clear Catridge Pool Filter. Pool 17'2" X 35'4"
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InyoPools Product Specialist  Posted: 10/19/2020 

yes, the W3C1200 can replace your Perflex DE filter.
 Reply

 Posted: 9/26/2020 

We have a 16 by 32 above ground pool how big should R cartridge filter be.
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InyoPools Product Specialist  Posted: 10/6/2020 

A 16' X 32' above ground pool would require at least a 90 square foot cartridge filter. For future commenters, you can refer to this guide for sizing an above ground pool filter: How to Size an Above Ground Pool.Filter
 Reply

 Posted: 7/27/2020 

That was very very helpful
 Reply

InyoPools Product Specialist  Posted: 8/21/2020 

You're welcome! Thank you for reading.
 Reply

 Posted: 7/26/2020 

I am needing to replace my cartridge filter for my above ground 18’ round pool. The cartridge size I have has been discontinued (c-7399). This cartridge has been rated for 100 square foot pool filters. I can find a 50 square foot one that looks to have the same dimensions but we are concerned it might not be enough filter. I can also find a 75 square foot that is 1/4 inch taller or a 181square foot that could work too. Is going up to the 181 going to stress the pump out?
 Reply

InyoPools Product Specialist  Posted: 9/8/2020 

If the 181 matches the exact dimensions, then that would be the ideal option. The larger you go, the higher the flowrate it can handle, and the longer you can go between cleaning. Going with a lower square footage filter could give you pressure problems.
 Reply

 Posted: 4/21/2020 

Hi! I’m replacing my DE filter for a Hayward Cartridge filter but no sure which one do I have to select. My pool is small: Width - 8’8”, Length - 19’, Shallow End - 3, Deep End - 6 based on this numbers I was able to calculate that is approximately 5,643 Gallons. Actually the pool has 1HP pump.
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InyoPools Product Specialist  Posted: 4/24/2020 

What id the model number of your DE filter? I can get a better estimate of what size you need by comparing a cartridge model to the DE you currently have.
 Reply

 Posted: 4/25/2020 

Thanks for your reply. Unfortunately I do not have that information. It is a very old WaterCO DE Filter installed back on 2005. Sorry to not able to provide additional information.
 Reply

 Posted: 4/9/2020 

I live in AZ and am looking to replace a sand filter with a cartridge or DE filter. Pool is about 25k gallons, pump is Hayward Super Pump 1.5 hp with about 30 ft of head. What is your recommendation for a filter?
 Reply

InyoPools Product Specialist  Posted: 4/15/2020 

For a pool that size, matched with a 1.5 HP pump, I'd choose a cartridge filter size of 125 square feet or higher. The plus side of going with the bigger filters, you can go longer between cleanings.
 Reply

 Posted: 3/28/2020 

Hi, I have a pool with 48,750 total pool volume with a 3 hp pump and a Hayward filter W3C4030 which has 425 sq ft of filtering. it seems as though the filter is too small for this system ? or else the pump is too big ? there is 2 1/2 piping on this system a 2 heat pumps and one gas heater all in Parallel each with valves tees and 90's and I don't know how many under going to the pool. Debating weather to buy a larger filter ?
 Reply

InyoPools Product Specialist  Posted: 3/31/2020 

I cannot tell what the issue is from your comment. Is there a back pressure problem? The Hayward Swimclear Cartridge Filter 425 sqft can handle 150 gallons per minute (GPM) flow rate, and can turnover 72,000 gallons in 8 hours. That is more than enough for that pool size.Also, how long have this pump and filter been installed together? If this is a recent pressure issue and they have been working fine for a year or more, then you may just need to clean the filter.
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 Posted: 3/28/2020 

I have a 12x24 oval pool and am looking to replace the cartridge filter system (the pump works fine, so only looking to replace the filter system). I have found some I like, but they talk about "square foot" and I'm not sure what that means.
 Reply

InyoPools Product Specialist  Posted: 3/31/2020 

What size is your current filter? Whether it be sand or DE, we can get an idea of what type of filter rate and capacity is required.
 Reply

 Posted: 12/25/2019 

Hi, I have a pool of 8x12, about 3,120-150 gallons. Have calculated a 3/4 pump. A 12” sand filter would be sufficient or what you recommend me?
 Reply