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How to Size a Pool Pump for Your In-Ground Pool

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When purchasing a new in-ground swimming pool, you need to determine what size pool pump is required. There is a tendency to purchase a bigger pump than what is necessary because people think bigger is better. However, not only does this lead to higher operating costs, but you may also be overpowering your filter system. As a general rule, you should have a pump that filters all the water in a pool in an eight-hour period. This page will show you how to select a pump that filters all the water in your pool in eight hours.

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Step 1

Rectangular Pools

Your first step is to determine the number of gallons of water in your pool. The formulas for calculating the gallons depend on the shape of your pool.

Measure the length (ft), the width (ft) and the average depth. The average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by two.

The formula for calculating the total gallons in a rectangular pool is Gallons = Length x Width x Average Depth x 7.5.

For example (see picture): your pool is 30 ft long and 15 ft wide. The pool's shallow end is 4 ft and its deep end is 8 ft. So, the pool's average depth is 4 plus 8 = 12 divided by 2. This gives you 6 ft. The pool's capacity is 30 ft x 15 ft x 6 ft x 7.5 = 20,250 gallons. Go to Step 5.

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Step 2

Round Pools

Determine the number of gallons of water in your round pool, measure the diameter of the pool and its average depth. The average depth is determined by adding the depth at the shallowest part to the depth at the deepest part and dividing by two.

The formula for calculating the total gallons in a round pool is Gallons = Diameter x Diameter x Average Depth x 5.9.

For example (see picture): your pool is 25 ft in diameter, the pool's shallow end is 3 ft and its deep end is 7 ft. So the pool's average depth is 3 plus 7 = 10 divided by 2. This gives you 5 ft. The pool's capacity is 25 ft x 25 ft x 5 ft x 5.9 = 18,428 gallons. Go to Step 5.


Step 3

Oval Pools

To determine the number of gallons of water in your oval pool, measure the longest diameter, the shortest diameter, and the average depth. The average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by two.

The formula for calculating the total gallons in an oval pool is: Gallons = Longest diameter x Shortest diameter x Average depth x 6.7.

For example (see picture): Your pool's longest diameter is 25 ft, shortest diameter is 15 ft and the pool's average depth is (3 + 7) / 2 = 5 ft. The pool's capacity is 25 x 15 x 5 x 6.7 = 12,563 gallons. Go to Step 5.

 

Step 4

Kidney Shaped Pools

To determine the number of gallons of water in your kidney-shaped pool, measure the largest width, the smallest width, and the average depth. The average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by two.

The formula for calculating the total gallons in a kidney-shaped pool is: Gallons = (Longest width + Shortest width) x Length x Average depth x 3.38.

For example (see picture): Your pool's length is 25 ft, longest width is 15 ft, shortest width is 10 ft and the pool's average depth is (3 + 7) / 2 = 5 ft. The pool's capacity is (15 + 10) x 25 x 5 x 3.38 = 10,563 gallons.


Step 5

Now that you have calculated the number of gallons in your swimming pool, you want to determine the required gallons per minute (GPM) you need to a pool pump to clean all the water in your pool in eight hours. To come up with this flow rate, simply divide your calculated gallons by eight.

For the Rectangular pool example, the GPH required is 20,250 gallons / 8 hours or 2531 GPH.

Most pool pump specifications are expressed in gallons per minute (GPM). So, to convert from GPH to GPM, divide your GPH by 60 minutes - 2531 GPH / 60 = 42.2 GPM.


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Step 6

Having calculated your required GPM, you next have to figure out the average Feet of Head for your pool pump. Check out our blog on How to Calculate Feet of Head. 

**Please note, we are currently reviewing our procedure for estimating feet of head. Current estimates are too high**

Step 7

You now have the information required to select the size of your pool pump. 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. 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 calculated above for a typical RECTANGULAR pool, we are looking for a pump that will handle 42GPM with a 47 Feet of Head. According to the chart for 50 Feet of Head (closest to 47'), we need a pump between 3/4 HP (31 GPM) and 1 HP (50 GPM). Since we always go for the higher GPM, we would select the 1 HP pump.

Step 8

The full performance page for the Hayward Super Pump can be found at this link, Hayward Super Pump. For the location of performance pages for other pump models, contact an Inyopools sales representative at 1-877-372-6038.

Step 9

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 encounters resistance at the filter. This will eventually burn out the pump motor and your filtration will also be compromised. We recommend selecting the filter so that it is oversized 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 10

There are a couple of other considerations that should be mentioned in your selection of a swimming pool pump. The above calculations are based on a basic pool configuration with no extra water features like: fountains, spas, waterfalls, solar heating, and in-floor cleaning systems. These features generally require higher GPM rates which equate to a higher HP pump. 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.

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(441 to 480 of 603)

 Posted: 10/29/2014 

Installing a 8,500 Gal pool, no features, 2" piping, 200 SF CS filter. Contractor is pushing a 2.0HP Jandy Variable Speed pump. I found a 1.0 Jandy Variable speed pump. Would want to run 24 hrs at lowest possible RPM for max efficiency. Salt system requires 20GPM min. so I guess that's lowest flow rate. Contractor says we won't be able to run pump at low speeds and need larger pump than 1.0 to run at lower RPM to save energy. Does this make any sense? Jandy support rep says nobody runs pumps lower that 1500 RPM regardless of size and that either will work. Feel like I'm in the twilight zone. Any advice? Should you oversize VS pump to run at lower RPM? Thanks
 Reply

InyoPools Product Specialist  Posted: 10/21/2014 

pump recommendation - If you can afford the initial cost, buy the smaller (~1.5HP) variable speed pump. It can save you up to 80% off you pool operating cost. For a single speed pump - a 1.0 to 1.5 THP pump is typically used on this size pool. Total HP (THP) is calculated by multiplying the HP x the Service Factor (SF) as shown on the motor label. Hayward and Pentair are the most popular brands.
 Reply

Anonymous  Posted: 10/21/2014 

I am in the market for a new pool (12,000 Galons) with spa. What will be the best pump I can get?
 Reply

InyoPools Product Specialist  Posted: 10/1/2014 

Stevo - Not sure how 2 motors would work. Don't think it would make sense to put them in series on the same piping. To get the GPM you need, I think each pump would need its own piping and filter system. I would recommend getting a large variable speed pump for your set up to regulate the flow as needed.
 Reply

 Posted: 9/30/2014 

Hi there i have a rectangle pool with 2 skimmer boxes and all plumbing 2 inch pipe and 30ft of head. The pool is a large pool with a pool volume of 80,000 gallons. So needing 166 GPM flow rate.
by your pump chart a 1.5 HP pump with 30 ft of head would give me 90GPM. So my ? is if i used to !.5 HP pumps would that equate to 180 GPM and be enough to run my pool or would i need bigger pumps. any information on pump and filter sizes would be much appreciated. many thanks Steve
 Reply

InyoPools Product Specialist  Posted: 9/29/2014 

Chris - Yes, I would recommend getting a VS pump, but, unfortunately, all the larger VS pumps require 220V.
 Reply

 Posted: 9/27/2014 

I have a 32' x 16' rectangular in ground pool 3' to 7' deep, with an attached spa, in-ground cleaning system and solar panels 75' from the pump (2" pipe). I estimate just under 20,000 gal. It currently has a 2.0 hp single speed Hayward pump that is 16 yrs old and leaking from the shaft into the motor. Since it is so old, I was just going to replace the whole unit. Do you recommend a variable speed pump with an in-ground cleaning system. It is wired for 110V and I do not want to rewire to 220V.
 Reply

InyoPools Product Specialist  Posted: 9/8/2014 

Dynakat - If you have an old pool, I'm guessing that you have 1 1/2" piping and if that's true, I wouldn't get a pump that's over 1 1/2 Total HP. Total HP is equal to the product of the values of HP and SF (Service Factor) listed on the label of the pump. For example, if your pump's HP is 1.0 and the SF is 1.5, your pump's total HP is 1.5 THP. With that size pump, I would get a 30" diameter sand filter. A good set would be the Hayward Super II Energy Efficient 1 HP Pump (1.5 THP) (SP3010EEAZ) with the Hayward 30" Pro Series Sand Filter (S310T2).
 Reply

 Posted: 9/7/2014 

I have a rectangular pool 20x40 with a deep end to around 10 ft. We have around 45000 gal. It is an old in ground concrete pool with only 1 skimmer and two ports. The pump and sand filter are around 20ft from the pool...what size pump would you suggest and sand filter size, not sure if our current sand filter is large enough but our pump was 1hp and just died.
 Reply

InyoPools Product Specialist  Posted: 8/16/2014 

jwsp - I would go with an  uprated 1 HP pump. The 1.5 HP pump is probably trying to move more water through your pool system that the 1 1/4" pipes can handle. See our guide on "How To Understand Pool System Water Flow Limitations" for more information.
 Reply

 Posted: 8/15/2014 

Very informative. I have an oval pool aprox. 25,000. Only suction line is 1 1/4 copper line from skimmer. All plumbing at pump and filter is 1 1/2. Pump when we moved in is 1.5 hp. Would I be better off replacing it with a 1 hp pump.

Thanks
 Reply

InyoPools Product Specialist  Posted: 8/15/2014 

Anthony Dal - You are correct. You will have to put in fittings at the pump to adapt your 1 1/2" pump port to your 2" piping.
 Reply

 Posted: 8/13/2014 

I have a 44,000 gallon pool with 2" pipe & 2 HP. I need new pump & being told with new pumps I can get a 1.5 variable speed pump which had 1 1/2 piping. I will need to put reducers. Is this correct
 Reply

InyoPools Product Specialist  Posted: 7/30/2014 

Sarah – First, the calculation for an accurate head of water is more complicated than what we present here. This guide provides a ballpark estimate for a typical pool setup which yours is not. I would doubt that you need 4-5 HP. Probably 3 HP would be adequate. Your issues are operational costs and equipment location. For costs, have you considered replacing your pumps or pump motors with variable speed pumps/motors. You can control the speed for initial startup [priming] and the back off to what you need for circulation and cleaning. This not only gives you HP [speed] flexibility but can save you considerable money on operational costs. See our guide on "How to Save Money Using a Variable Speed Motor".I would recommend the larger 3 HP pumps like the Pentair Intelliflo or the Hayward Ecostar. Can't suggest much on the equipment location. You might try the VS pumps first. Even if you decide to move the equipment, the VS pumps will decrease your operation costs considerably. Also you might look at putting in check valves between the pump(s) and the pool to keep the lines from emptying when the pump is off. Should help priming.
 Reply

 Posted: 7/29/2014 

Hi- I have a 44,000 gallon kidney shaped pool & in-ground spa, built in the early 1990's. We have a higher than typical bather load (4-8 kids daily for several hours). Our pool equipment is located about 7 feet higher than the pool water level. We have a Nautilus DE filter. Our pumps do not consistently prime so we manually run the equipment daily to keep the water clean. Several pool contractors scratch their heads as to how to fix our pool. A few have recommended relocating the pool equipment so it is level with the pool water (or up to 3 feet lower). Recently an engineer commented we likely don't have to much head for our 1.5 HP pump. Doing the math from your chart, we'd need a 4-5 HP pump. Would it be wiser in the long run to have the equipment at water level, or upgrade our HP for the pump? Our energy costs are very high (about $.30/kilowatt) but we're being quoted about $5k to relocate the equipment. Help!
 Reply

InyoPools Product Specialist  Posted: 7/29/2014 

Damon - If you have 2" piping, you could go with the 2 HP pump with the option of scaling back to 1-1/2 HP by changing the impeller (and maybe diffuser). If your pipes are 1-1/2", I would not recommend going to 2 HP.
 Reply

InyoPools Product Specialist  Posted: 7/28/2014 

nancy - Check you sand level. You state that your filter is 22" with 250 lbs of sand. The spec I see on that filter state 150 lbs of sand. If you don't have enough space between the top of the sand and the top of the filter tank, you won't provide enough room for filtering and backwashing properly. And you may be overloading your pump.
 Reply

 Posted: 7/28/2014 

Thanks for your reply from 7/24. One last thing, with such a long run to the solar heater on my roof, would it make sense to go with a 2 hp and then downsize the impeller if the filter/equipment is getting too stressed. My understanding with impellers is that you can downsize them but not the other way around. Thanks again
 Reply

 Posted: 7/27/2014 

I have a 16x32 inground pool with approximately 19,000 gallons
Replaced my old hayward filter 3 years ago with a waterway of same
size. 22" 250 lb sand filter. Has been noisy since day one. This year
replaced my hayward super pump 1 hp with sf of 1.10 with a hayward maxflo xl 1 hp with 1.25 sf. Also changed sand and inspected laterels, all fine. Filter still noisy. I have 40 feet of head with 1 1/2 in plumbing. Not filtering properly either. Any suggestions? Also there are no air leaks that I can find either.
 Reply

InyoPools Product Specialist  Posted: 7/24/2014 

Damon - For your size pool and connection to a solar panels on the roof, I would recommend a 1 1/2 HP full rated motor. Full rated motors have Service Factors {SF}of greater than 1.25.
 Reply

 Posted: 7/24/2014 

Very informative. Thanks. I am trying to size a single speed motor replacement for my filter pump. The catch is that the pump is connected to a solar heating system on the roof. The distance from the pump to the pool is only 19ft but from the pump to the solar on the roof is 150ft with 10ft of that being vertical up to the roof. I'm figuring a 2hp motor will work. Any thoughts greatly appreciated. Thanks.

Pool is 13,000 gal
2" plumbing
 Reply

InyoPools Product Specialist  Posted: 7/17/2014 

CCWP - Your pool has about 2,250 gallons so I would recommend the smallest in ground pump you can get. The Sta-Rite Super Max 1/2 HP is a good, quiet and economical choice for a main brand (reliable) pump.
 Reply

 Posted: 7/16/2014 

I am looking for a pump for an inground baby pool measuring 10'x 20' x 18"deep. The pump will be located within 5' of the pool and level with the pool surface. Any suggestions?
 Reply

InyoPools Product Specialist  Posted: 7/8/2014 

DASMan- Yes, a 2-speed motor can save you about 25% in operation costs; a variable speed pump 75 to 80%. See our guide "How to Save Money Using a Variable Speed Motor" for more information.
 Reply

 Posted: 7/8/2014 

Thanks for the recommendation. Would there be any benefit to using a two speed or variable speed pump keeping any eye to power efficiency?
 Reply

InyoPools Product Specialist  Posted: 7/8/2014 

DASMan - For your size pool, 28' round and your preference for a IG pump/filter set, I would recommend a Hayward Super Pump 1.5 HP SINGLE Speed W/ DE4820 48 Sq. Ft. DE Filter. This pump has a 1.0 SF so the true HP is 1.5 HP. The pump has 1.5" ports but the filter has 2" ports. You can reduce the filter ports to 1.5" with a reduction fitting available at any HW store.
 Reply

 Posted: 7/6/2014 

Hey there I have a question that I hope you can shed some light on. I have a 28' round AG pool and the pump seized. The manufacturer doesn't make that pump any longer and because of where the inlet of the filter is, the new pumps will no longer line up. Instead of going with traditional AG filter kits, I would like to use an IG pump and filter. I have one skimmer and two returns all hard plumbed with 1 1/2" pipe; the skimmer is about 15" away from where the pump will be located and I do have a heater. What size pump do you recommend and what size filter. I prefer to use D.E. As I have had great experience with that in the past.

Thanks in advance for your help.
 Reply

InyoPools Product Specialist  Posted: 6/26/2014 

Ccbcr2000 - A 1 HP should be fine for your size pool. And I would recommend a 2-speed pump for operational cost savings.
 Reply

InyoPools Product Specialist  Posted: 6/26/2014 

poolenvy - The 1.5 HP pump is a good size for your size pool. Did you use pool sand? Try backwashing and rinsing the sand 2 or three times to clear whatever is in the sand.
 Reply

 Posted: 6/25/2014 

I have an above ground pool that was put in with 1 1/2 pipe. It has a bottom drain as well as 2 skimmer baskets. I had a 3/4 hp pump and when it went bad we replaced it with a 1 hp. This pump now needs to be replaced. I have read about the dual speed pumps and I am uncertain what to buy now. Do you recommend dual speed or single? Someone told me I needed a 1 1/2 hp dual motor. I think this is too much since my pool only has 8640 stallions of water. It is rectangular 12 x 24 and 4' deep.
 Reply

 Posted: 6/25/2014 

I have a Hayward s244t pool filter and a 1.5 pump, for a 23000 gallon pool, replaced the sand and laterals but still seems like their is sand coming into the pool. cloudy water but chemicals are all normal levels, pump was off for at least 1-2 days and pool was clear could see drain, turned on pump and was cloudy again, CAN'T SEE drain. we use to have a 3/4 hp pump, do you think the pump is too big?
 Reply

InyoPools Product Specialist  Posted: 6/17/2014 

justin - I assume you are talking about a 1 HP Pentair Supermax since you seem to be going with the example above. That pump will work well with either the c900 or c1200 filter. I would go with the larger filter, if possible. It will last longer and will require less cleanings.
 Reply

 Posted: 6/15/2014 

I pretty much have the same situation you have listed above. 15x30 pool and the piping(2in) is around the same distance. Right now I have a Pentair Challenger pump. I am going to replace my pool filter to a Hayward c900 or c1200(opinions please) and I have a brand new Pentair Supermax. My current filter is broken and not fixing and the pump so far has no problem, but old. Will the Supermax and the c900-c1200 work fine together? Dont want to re-pipe but once.
Thanks
 Reply

InyoPools Product Specialist  Posted: 6/14/2014 

Kate - With 1 1/2" piping you shouldn't go over a 1 1/2 HP size pump. If you can change out the piping to 2", you could go to 2 HP. Depending on the rebate guidelines; you may be able to use an Energy Efficient [EE] pump, a 2 speed pump or a variable speed pump.
 Reply

 Posted: 6/13/2014 

Hello, my local utility is offering $400 rebates for high efficiency pool pumps and ours is at end of life. I need some help ordering the right pump. Can you help?

Here are the facts:
I have a 33,000 gallon pool
One intake/skimmer about 10 feet from pump
Hayward 24" sand filter
1.5" pipes

What else do you need to know? Which pumps do you carry that would fit the bill?

Thanks, Kate
 Reply

InyoPools Product Specialist  Posted: 6/13/2014 

bucky - Yes, you can use an in-ground pump and filter system on an above ground pool. You just cannot use an above ground pump and filter system on an in-ground pool.
 Reply

InyoPools Product Specialist  Posted: 6/12/2014 

Katmathis - If your old system has 1 1/2" piping, you should not go above 1 1/2 HP. The 2 HP pump would generate more GPM than the piping could handle. If you have 2" or 2 1/2" piping, you could go to a 2 HP pump.
 Reply

 Posted: 6/12/2014 

can i use an inground filter and pump for a 27foot above ground pool
 Reply

InyoPools Product Specialist  Posted: 6/12/2014 

Andrew - Can't say why the grids broke. Sometimes the pump is too large for the filter, but the DE 4800 has sufficient GPM for a 1 1/2 HP pump. Check to make sure the manifold and base that hold the grids are sound.
 Reply

 Posted: 6/11/2014 

Hello! We have an OLD (early 60's) rectangular inground pool that is 20 x 40 and 10 feet at the deepest point with the skimmers and jets being about 60 feet from the pump. We currently have a 1.5 hp pump that we are replacing. Should we consider a 2 hp?
 Reply