How To Size a Pool Filter

WRITTEN BY:  Inyo Pools

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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.

Step by Step


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.

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


(1 to 40 of 70)

Eric  Posted: 11/28/2018 

Looking for a pool pump and filter replacement. My pool is 16x32 at 19,000 gallons. I have a solar heater as well. Currently I have a SVL56 waterway 1.5hp and 1.10 SF pump and a prclean pccf-200 filter rated at 75gpm. I am looking to replace this combo with a 1.65hp Haywood SP2303VSP maxflo and a Haywood C17502 SwimClear Plus pool filter. Will this combo be an adequate replacement for what I currently have?

InyoPools Product Specialist Robert M.  Posted: 11/28/2018 

Hello Eric - Yes, the Hayward Max-Flo VS SP2303VSP and the Hayward Star Clear Plus C17502 would be great replacements for your 19,000 gallon pool.

Anonymous  Posted: 11/5/2018 

I have an above ground doughboy pool that is 21 ft wide by 41 ft long and is3 feet deep on one end and 6 feet deep on the other end. What pump and filter would you recommend?

InyoPools Product Specialist Robert M.  Posted: 11/6/2018 

Thank you for contacting Inyo. We'd recommend the Hayward model CC15093S for your 21'x41' above ground pool. This system has a 1.5HP pump and a 150 square foot cartridge filter. The pump comes with a standard 3-prong plug. We also carry a version with a twist-lock plug.

Matthew  Posted: 8/7/2018 

Hello Chuckee - As we mentioned in step 4 of the guide, the flow rate of a pump is determined not only by its horsepower but by the plumbing system's feet of head. A 2 HP pump may only push 55 gallons per minute (GPM) if the feet of head is high enough. Where as on a different pool, a 1 HP pump can push 90 GPM. But to answer your question, you need to know the feet of head of your system and the flowchart of your specific pump to determine if it will match the Hayward C1200. Luckily, the C1200 has a flow rating of 120 GPM, making it pretty hard for any pump to test its limits.

Matthew  Posted: 7/20/2018 

The Hayward EcoStar Owner's Manual states the following regarding the Drive Error: Prime Failed:

Indicates that the pump was not able to prime within 15 minutes of startup.
Plumbing and fittings should be checked for potential air leaks and corrected.

Priming issues could be an issue with blockages or air leaks. A checklist of things to check on your plumbing system can be found in this guide: How To Determine Why a Pool Pump Won't Prime. Also, try cleaning the cartridge to alleviate any pressure issues.

Inyopools  Posted: 7/19/2018 

Hello Jeff - Something like the Hayward model S166T92S would be sufficient for an 18' above ground pool. This is a 1HP pump with a 16" sand filter.

Inyopools  Posted: 7/18/2018 

Hello Janet - We would recommend a sand filter that is 18" or larger.

Mel  Posted: 7/17/2018 

I'm not sure if our new pool filter has been properly sized. Our old pool filter was replaced with Pentair CC100 a month ago, and we got the Hayward EcoStar Variable Speed pump. Our inground pool is bean-shape about 39ft x 18ft with spa. We also got a new heat pump 35000btu. The issue we been experiencing, the pool pump stops with Priming Drive Error about every 15 minutes when we set the valves to flow to the spa. We also noticed that the initial filter gauge was about 22 psi then goes to about 27psi to 30psi. Usually the gauge is at 8psi when the valve is set to waterfalls and about 12psi when set to main pool only. What do you think is about ISSUE? I'm guessing it might be the CC100 being too small. I appreciate any recommendation. Thanks, Mel

chuckee  Posted: 6/17/2018 

what is the biggest pump I can safely use on a hayward 120 sq.ft.filter without causing damage

Jeff  Posted: 5/26/2018 

Hello we have a 18 foot round above ground pool that is 4 feet deep. We were looking to get a sand filter and pump. What do you suggest for which sand filter and pump combo to get? We were looking for hayward. Thank you!

Janet  Posted: 5/18/2018 

I have an 18’ x 52” round pool. I bought a 1.5 hp pump and it blew the sand from my filter into my pool. What size sand filter do I need to get?

Inyopools  Posted: 5/18/2018 

Hello Lynn - You can get a filter without a pump. We'd recommend the Hayward C751 for your 27' above ground pool.

Lynn  Posted: 5/17/2018 

We have a 27' diameter pool 5 foot deep. We currently have a sand filter with a 1.5HP Hayward motor (which we bought less than 2 years ago). We want to go to a cartridge filter. Can we buy a cartridge filter system without buying a new pump motor? If so, which one do you recommend for our pool?

Inyopools  Posted: 5/17/2018 

Hello Brooks - Your pool size would hold about 25k gallons. The Hayward S210S would be a little undersized. We would recommend the S244S.

Brooks  Posted: 5/16/2018 

I have an 18x33 in ground pool. depth goes from 4 - 7 feet. What size hayward filter do you recommend? is the S210S sufficient or should I go with S244S?

Inyopools  Posted: 5/10/2018 

Hello TKG - Even though the DE2420 is advertised as an inground pool filter, it can be used on above ground pools. I agree that you would be stepping down if you went with the EC50. I'm not a fan of the DE "fingers" inside the EC50. If you ever have to replace the full set of fingers, it costs as much as a complete filter.

tkg  Posted: 5/9/2018 

hello, my above ground pool is 15x26 and 52in deep. so I generally estimate 12000 gallons. I have a 1.5HP Hayward power-flo lx pump, and a Hayward Pro-Grid de2420. The base is cracked so I have to replace the filter and am getting mixed reviews for what to replace with. Apparently this model filter is not commonly used for above ground pools, and I have been directed to a Hayward EC50. Seems like such a step down, but also much cheaper. Thoughts?

Inyopools  Posted: 4/30/2018 

Hello KR - Because of the 2.25HP pump, we'd recommend something like a Hayward S310T2. This is a 500 pound sand filter with a 30.5" diameter tank.

kr  Posted: 4/30/2018 

have a 15X30 inground pool approx 20,000 gallons with a 2.25 HP pump. I'm replacing my DE filter with a sand filter. Recommendation on size and or make/model of sand filter to look at please.

Inyopools  Posted: 4/17/2018 

Hello Heather - The 21" Hayward S210T sand filter would be sufficient for your 18'x34' above ground pool and it will work with the SP1593 pool pump.

Heather C  Posted: 4/13/2018 

Hello. I have an above ground 18'x34' pool. We have a 1.5 HP Hayward SP1593 pump and we need a new filter. Our old filter is a sand filter (Hayward S230T) but that is only sold as a combo filter/pump. Can we get the Hayward S210T filter to use with the SP1593 pump? I think they are both 200lb. sand filters. Not sure what the 21" and 23" difference means. Anyhow, what filter do you recommend?

INYOPools  Posted: 4/6/2018 

This would partly depend on the pump model and its horsepower, as mentioned in the how-to. For most most pools that size, a 75 sq. ft. cartridge filter would do the job.

Luis Rivera  Posted: 4/6/2018 

HI i wanted to ask what size Cartridge filter i need for a 10x16 oval above ground pool.

Inyopools  Posted: 3/9/2018 

ax3bl4d3 - We would recommend a Hayward Star Clear Plus 90 Sq Ft. Filter 1 1/2" Ports for your 1.5 HP Hayward pump.

ax3bl4d3  Posted: 3/7/2018 

16x32 above ground with 1.5hp hayward pump. what size minimum cartridge filter should I look at?

Inyopools  Posted: 3/7/2018 

Anonymous - Yes, you can use a C3030 cartridge filter with a 1 HP above ground pump. It is much larger than you need, but there is no limit to the upper size of a filter. You just won't have to clean it as frequently.

Anonymous  Posted: 3/6/2018 

Can I put a C3030 hayward cartrige filter with an aboveground pool with a 1 hp pump?

Inyopools  Posted: 2/20/2018 

Drodn - Your pool contains about 16,875 gallons of water. For this size pool, I would recommend a 1.5 Hp pump like the PureLine Prime Pool Pump and a Hayward 27" Sand Filter with Top Mount Valve.

Drodri  Posted: 2/18/2018 

I have a 15' X 30' fiberglass pool. The depth runs from 3.5' to 6' so I assume average depth at 5' to be conservative. Would a 1.5 hp pump and a 21" sand filter be the correct size for my pool? Thank you.

Jaki  Posted: 1/16/2018 

Hi, I have a 22X52 Colman above ground pool and trying to determine what size sand filter. Thanks !

Inyopools  Posted: 11/13/2017 

Joe - A Pentair 1 1/2 hp VS pump would be a good choice for your size pool with the roof mounted solar panels. You didn't say why you hate your current filter other than having to clean it twice a week. If your want to switch to a sand filter, I would suggest something like a Hayward Sand Filter with Top Mount Valve 30 Inch Tank - S310T2.

Inyopools  Posted: 11/13/2017 

Scott- You can never have a filter that is too big for the pump. Many dealers even recommend upsizing the filter by 25% so there is no chance of the pump blowing out the filter. A larger filter just means that it will last longer between cleanings.

Joe  Posted: 11/12/2017 

I am looking to change out my pump and filter for my 15000 gal pool. I have 6 solar panels on my roof 10 to 12 feet above the pump and 2 little water sprays at the pool. I currently have a 1hp Starite single speed pump and a 150 Starite filter. I am cleaning this filter twice a week and hate it. Would like to know if a Pentair 1 1/2 hp VS pump would be sufficient and what size filter would I need. Piping head without solar is approx. 40 to 50 ft.

Scott  Posted: 11/4/2017 

I have a dayton 1 1/2 HP pump grainger #5PXC5A thats rated at 10ft/77, 40ft/51.7. I need a new filter and have been offered less than 6 months old at a very good price but I'm afraid its too much filter for the pump. It's a Hayward Stay Clear model CL1200, can you tell me if it will work?

InyoPools Product Specialist Dennis R.  Posted: 9/28/2017 

Anonymous (3600 gal pool) - Your cartridge in your filter may be clogged with oils and chemicals that are difficult to wash out of the folds. If you haven't changed your cartridge this year, you might buy a new one. If you want to switch to a sand filter, look at the next size up, 35 GPM. Your current filter is 25 GPM (1500 GPH).

Anonymous  Posted: 9/26/2017 

Hello, I have a roughly 3600 gallon frame pool. It is running a 1500GPH filter cartridge pump (Type c filter). We have fought with cloudy water and chemistry all summer, mainly chlorine, so we added a SWG. It was great for a couple weeks, now cloudy again. All numbers within range. Is our filter too small? I'm cleaning it every other day! Could a sand filter with higher GPH help?

InyoPools Product Specialist Dennis R.  Posted: 9/25/2017 

maurice - I'd recommend a sand filter like Hayward's Sand Filter w/ Top Mount Valve 27 Inch Tank 2" Valve - S270T2 for your size pool.

maurice  Posted: 9/23/2017 

Hi, I have a 15000-18000 gal pool. I am trying to replace my cartrige filter with a sand on. what size do I need? (1.5hp pump. thx

InyoPools Product Specialist Dennis R.  Posted: 9/7/2017 

mike - See our article on "Pool Filter Information" for a description of the three most common filter types.