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

#### WRITTEN BY:  Inyo Pools

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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.

### Step 1

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.

For a RECTANGULAR 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.

### Step 2

For a ROUND SWIMMING POOL:

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

For an OVAL SWIMMING POOL:

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

For a KIDNEY-SHAPED SWIMMING POOL:

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 how many gallons per hour (GPH) you need to 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 swimming pool example the GPH required is 20,250 gallons / 8 hours or 2531 GPH.

### Step 6

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.

### Step 7

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 8

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 9

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 10

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 11

There are a couple of other considerations that should be mentioned in your selection of a 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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InyoPools Product Specialist  Posted: 7/23/2013

oyster56 - I don't see a motor replacement at 1.25 THP, but based on your information, you could probably use a motor with 1.1 or 1.0 THP. The 1.1 THP motor is a standard uprated motor, UST1102. The 1.0 THP motor is an Energy Efficient (EE) motor, UCT1102. The EE motor is \$40 more but would save you 20% on operating costs. Also since these both are slightly smaller motors than your old one, you will have to buy a smaller impeller. And, for any motor replacements, you should buy a new shaft seal.

Posted: 7/23/2013

We have a pool that just about exactly matches your average pool but it has only one drain and one skimmer, which are an average of 30 ft. away from the pool pump. We currently have a A.O. Smith Century Centurion 1 HP motor with an SF factor of 1.25, which has reached the end of its life. This pump motor is on a Jacuzzi Magnum 1000 pump. Is a replacement with THP of 1.25 sufficient or over or under our needs? There are no additional features such as waterfalls using the pool pump's capacity. Although I favour a VS pump for the quiet and the lower environmental impact, given our modest electricity costs and a short swimming season of less than three months, we will probably stay with a single speed pump motor. Thoughts? Suggestions? Thanks.

InyoPools Product Specialist  Posted: 7/18/2013

Mike - Your pool holds about 10,000 gallons of water. A 1 1/2 HP pump should be sufficient to handle circulation for this size pool and your waterfalls.

Posted: 7/17/2013

I am having a 27x12 fiberglass pool installed. The deep end being 5'. I am also having a three tier waterfall with 1 shear decent in the middle and 2 18" shear decents on either side. I am having a 1 1/2 hp pump installed. My question is should I get a second pump to run the waterfalls. The pump will be located 15' from the skimmer.

InyoPools Product Specialist  Posted: 7/17/2013

MM - For a head of 11' you would need a 1/2 HP Hayward Super Pump that would provide 55 GPM. This is overkill but this is the smallest pump we sell. For a head of 67' the charts show you would need a 1 HP Hayward Super II Pump (different class of pump) which provides 35 GPM. The next lower pump, 3/4 HP, is right on the edge of providing 19 GPM for 67' of head and the manufacturer recommends going up to the next level.

InyoPools Product Specialist  Posted: 7/16/2013

Bjtex - Yes, you could use a 1 1/2 HP pump but you're on the edge. You could hedge your choice a little by getting a 1 1/2 HP pump with a SF of 1.10 or 1.25 to get a slightly higher THP. THP = HP x SF. If you are concerned about operating cost and can afford the initial pump cost, you should look at buying an Energy Efficient (EE) pump or a 2 speed or variable speed pump.

Posted: 7/16/2013

I am building a small inground splash pool of size 13' X 8' with 3' depth. This will contain 2300 gallons of water. I have two options for placing the pump ; one nearby with head of 11' and the other at a distance with head of 67'. What capacity of pump and also the pump size is recommended in each of the two cases with flow of 19 GPM? Appreciate urgent help. Thanks

Posted: 7/14/2013

I have a 30K In-ground pool with 40 ft of head and 2 in water lines Could I use a 1.5 hp pump. I currently have a 10 yr. old 2 hp pump that's very costly to run...

Thanks

InyoPools Product Specialist  Posted: 7/8/2013

volts/amps/watts - A pool motor's volts/amps/watts are generally defined by the HP of the motor. With little exception, pool motors use either 115V or 230V. That is defined by the power available at the house. Amps (and Watts) are directly related to HP. The more HP a motor has, the more Amps/Watts it will use. Some EE motor are designed to be more energy efficient than their stand counterparts and might use 20% less Amps/ Watts for the same HP.

InyoPools Product Specialist  Posted: 7/8/2013

Glenn- Your main limitation is your pool's pipe size of 1 1/2". For your volume of water you could probably use a 2 THP pump but your piping should not use anything over 1 1/2 THP. Note that's real or Total HP [THP] which is the product of HP and Service Factor [SF] - see motor label. For example, a motor with a labeled HP of 1.5 and a SF of 1.4 has a real THP of 1.5 x 1.4 or 2.1 THP. If you have the option of changing out your piping for 2" or 2 1/2" pipes, you could use the larger pumps.

Anonymous  Posted: 7/7/2013

I have a 14 x 28 rectangle pool, I know I need a 1hp pump, but how do I know how many volts/amps/watts ?

Posted: 7/6/2013

I have a 24x48 inground liner pool (50,000gallons). I have to run the pump 24/7 to keep clean. There is 2 stair returns, and 2 returns in shallow end for a total of 4 (2 lines leave pump and turn to 4). I then have 2 skimmers and one bottom drain. All the pipes are 1.5 inch. 500lb sand filter and a 1hp motor. What changes do I need to do so I don't have to run pump all day and night and keep a clean pool? Any advice would be super helpful! Thank you.

InyoPools Product Specialist  Posted: 7/2/2013

anna - This guide provides an estimate for a typical pool. With your pool's extra returns and drains, you could go with a 1 1/2 THP pump. A 2 THP pump is probably too big. However, if you have 2" piping in your suction and return lines, you could go with a 2 THP pump and if you find it's too much you could back it off by substituting a smaller impeller. Note make sure you are looking at real or Total Horse Power (THP) which is the product of HP and Service Factor (SF) when selecting a pump size. Some pumps labeled 2 HP can actually be 2.5 THP if the SF is 1.25.

Posted: 7/1/2013

I have rectangular pool with 4 drains along the bottom every 12 feet or so. My pool is 52' long by 8' wide by 6' deep. It has around 20 returns going all the way down both ends of the pool and 1 at each end. I currently have a 1 hp pump and going by your calculations, that is exactly where I should be but the returns at the far end of the pool barely have a drizzle coming out of them. I also get terrible suction while vacuuming the pool. I want to go to a 2 hp pump just because I am afraid of not going big enough. Do you think that a 1 1/2 hp would be enough?

InyoPools Product Specialist  Posted: 6/29/2013

terry - For your size pool with a spa and water features and 2" piping, many people use a 2 HP pump.

Posted: 6/28/2013

i have a 20 x 40 33,000 gal. inground pool what size pump do i need ?

Posted: 6/22/2013

I thought that determining pump head simplisticly was to measure return pipe runs from the pump to the pool instead of measuring pipe runs from skimmers and drain. If I use the measurement from skimmer and drain my head is 20; if I use the measurement of return lines my head is somewhere around 50-60. I guess I'm missing something here.

InyoPools Product Specialist  Posted: 6/14/2013

Steelers7 - Sounds like going to a 1 1/2 HP pump is a good option. Your 600 # Sand filter will support the increased GPM flow and your pool is sized for it. Also, this size motor will support the addition of a new waterfall. When you move the pump and filter out 20', make sure that the wiring from the circuit breaker to the pump is at least 14 gauge for 230V or 12 gauge for 115V supply power. Consider buying an Energy Efficient (EE) pump for operational cost savings of 20%.

Posted: 6/12/2013

Just want to know, I have a 17k inground pool with a heyward 600 lb sand filter. I want to later add a water fall using the pool water and possibly move the pump and filter approx. 20' away from where it is now. It is approx. 8' from the skimmer. Can I use a 1-1/2 hp pump wothout damaging anything right now as it stands. I currently was using a 1 hp until the motor gave out. Help.

InyoPools Product Specialist  Posted: 6/2/2013

Jc - We generally recommend a pump with 1 1/2 Total Horse Power (THP) for a pool your size. THP is the product of HP shown on the motor label times its Service Factor (SF) printed on the label.

InyoPools Product Specialist  Posted: 6/2/2013

sendmiller - We would also recommend a 1 1/2 THP pump for your size pool. Be aware that when you are looking for a 1 1/2 HP pump you need to look at Total Horsepower (THP) which is the product of HP and Service Factor (SF). If you look at your motor label, your HP might read 1 HP and the SF might read 1.5. Your motor's THP would be 1 x 1.5 or 1.5 THP.

Posted: 6/2/2013

Hi im trying to change my pump & piping on my inground pool..my pump is rusted i cant see the pump info..here's my pool info i got 20k gallons 1 skimmer & 1 return ,1.5" pipe will change to 2"...i measure the feet of head about 20 feet & will put three 90 deg fitting once change...my filter is sand w/ filtration area of 2.6 ft , filtration rate of 20 gpm/ft,filtration & backwash design flow rate of 52 ..pump info's 3/4 hp w/true hp of 1.22 @ max,feet of head of 22 & flow rate of 50 gpm.. Or 1 hp w/true hp of 1.65 @ max,feet of head of 24 & flow rate of 54 gpm..do i go 3/4 hp or 1 hp?...thanks

Posted: 6/1/2013

We have a 35,000 in ground pool. We currently have a 1 hp hayward super pump. We have a slide that uses water from the returns to operate. We did not have the pool put in, it was here when we bought the house. Our pump is dying and needs replaced. Local pool store tells us we should have a 1 1/2 hp pump. We are not sure and hesitant to go up for fear this would mess up our system. We have a polaris cleaner but that runs off a booster pump. Can you help recommend if we should stick with 1 hp or upgrade to 1 1/2 hp? Our pipes are 1 1/2 inch if that makes a difference. Thank you for any advice you can give.

InyoPools Product Specialist  Posted: 5/29/2013

Alleng - We recommend a 1 1/2 HP pump for an Above Ground pool holding 17,000 gallons of water.

Posted: 5/27/2013

My above ground pool is a little over 17000 gallons. Not sure how to figure the head on it. i only have one skimmer that is about 4 feet from the pump. My pump died so I'm trying to figure out what would be the appropriate size pump to replace it with. This one was a 1 hp.

InyoPools Product Specialist  Posted: 5/23/2013

Bart - We would recommend a 1 1/2 THP pump for your size pool. You have to look at Total HP (THP) when sizing a pump for your pool. THP is equal to HP x Service Factor (SF) as shown on your motor's label. Your old B129 has a THP of 1.95 which was probably larger than you needed. The Tristar EE pump is a good option. I would recommend the 1HP motor (THP 1.85). But a better option, if you can afford the initial cost, is the new Hayward Variable Speed (VS) Super Pump. It is rated at a maximum 1.5 HP. About half the size of the original VS pumps. The initial cost is higher but you can get that back in cheaper operating costs in the first year. And because they are sealed, they will last 2 to 3 times as long as a standard motor. See your guide on How to Save Money Using a Variable Speed Motor for more information.

Posted: 5/22/2013

My pump motor just failed and I've decided it's time to replace the entire pump. The motor was a B129 (AO Smith) 1.5hp that was not the original motor on a Hayward Northstar pump. I have no idea what the original motor was as it failed years ago and a technician replaced it. The pool is about ~17000 gallons with 50ft avg head with a raised spa with waterfall; the filter is a Hayward 4820 DE. Based on what I can calculate, it sounds like the B129 may have been overkill but I'm not sure how to account for the spa and waterfall. I'd like to replace with an EE model and am considering Tristar or equivalent. Do you have any recommendations? Thanks in advance.

InyoPools Product Specialist  Posted: 2/24/2013

Frank - In-ground and above ground pool pumps are designed differently. Since an above ground pump is installed below the water level, it can rely on gravity to feed water into the pump. An in-ground pool pump is installed above the pool's water level and is designed to suck water from the pool to the pump.

Posted: 2/22/2013

Why cant you use a above ground pool pump instead of a inground?

InyoPools Product Specialist  Posted: 2/11/2013

JayinFL - I would go with a third option, the SP3207EE model - Total HP = 1.39 (HPxSF). This model would deliver the same Total HP as your previous motor. The SP2010EE has a Total HP of 1.85 which I think would be overkill for your setup.

Posted: 2/11/2013

OK...here it goes. I have calculated my (kidney-ish) pool at 11,560 gal. Which gives me a turnover rate of 24 GPM. My filter is rated to 127 GPM. I have also calculated the Feet of Head at 47. Using the TriStar charts, it shows I would need a SP3205EE pump. I have a 5 panel solar heating system total run to and fro is 228ft(11ft is vertical to roof) and 4 deck jets with about 102ft of total piping. The existing (fried) pump is a Jandy JHPU1.5 with a 1hp (1.4sf) rated motor. Considering all factors, would I be better off with SP3210EE pump?

InyoPools Product Specialist  Posted: 2/11/2013

m.fed67 - With your size pool and no water features or suction cleaner, I would stick with the single speed pump as you suggest.

Posted: 2/9/2013

Hello- I have a 12,000 gal pool with no water features and a dying 3/4hp Hayward pump. I like the idea of an efficient VS pump like the Intelliflo. However since my pool is small, with minimal needs, I would probably run it on the lowest speed all the time so is there really any benefit to having a VS pump? Thank you.

InyoPools Product Specialist  Posted: 9/4/2012

ttiger - You have a large pool and if you have other water features, you may need your current size pump. I assume that the pump was sized to your pool. If you are trying to reduce costs, I would suggest looking at a 2-speed or a variable speed pump or motor. See our guide on variable speed motors for potential savings.

Posted: 9/3/2012

Help please. My pool is 36,0000 gallons. I currently have a Pentair Superflo 2hp which is dying. I need to replace. I want to know if I can get by with a smaller hp pump. I have five solar panels on the roof if that makes any difference, and a freeze defender (not sure if that makes any difference either. Your help is very much appreciated. Also, I have a Polaris pool cleaner and not sure if the hp size affects that.

InyoPools Product Specialist  Posted: 7/3/2012

watergirl - We will have to look up your impeller information in our files. Please give us a call.

Posted: 6/30/2012

For years I had a DE filter, loved it. after it died my pool service company changed over to sand filter, hated it. they changed out the impeller. Now back to DE but not sure my impeller size is correct. Is there any way to determine that? Seems like I have to run longer but never really catch up.

InyoPools Product Specialist  Posted: 6/23/2012

Trut,
I'm going to have to take another look at our calculations on this guide. Generally for your size pool, 19,000 gallons, we recommend a pump size of 1 to 1 1/2 HP.