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

Written by:  Danny Rhodehamel

When purchasing a new in-ground swimming pool, you need to determine what size pool pump is required. There is tendency to purchase a bigger pump than is necessary thinking bigger is best. 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 8 hour period. This page will show you how to select a pump that filters all the water in your pool in 8 hours.

Tips & Warnings

Things You'll Need

Step by Step

Step 1
gallons of water in pool

Your first step is to determine the number of gallons of water in you pool. The formulas for calculating gallons depend on the shape of your pool. For a RECTANGULAR POOL, measure the length (ft), the width (ft) and the average depth. Average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by 2. The formula for calculating total gallons in a rectangular pool is: Gallons = Length x Width x Average Depth x 7.5 Example (see picture): your pool is 30 ft long and 15 feet 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 = 6 ft. Pool's capacity is 30 ft x 15 ft x 6 ft x 7.5 = 20,250 gallons. Go to Step 5

Step 2
round swimming pool

ROUND SWIMMING POOL - To determine the number of gallons of water in your round pool, measure the diameter of the pool and its average depth. Average depth is determined by adding the depth at the shallowest part to the depth at the deepest part and dividing by 2. The formula for calculating total gallons in an oval pool is: Gallons = Diameter x Diameter x Average Depth x 5.9. 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 = 5 ft. 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 swimming pool

OVAL SWIMMING POOL - To determine the number of gallons of water in your oval pool, measure the long diameter, the short diameter and the average depth. Average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by 2. The formula for calculating total gallons in an oval pool is: Gallons = Long diameter x Short diameter x Length x Average depth x 5.9. Example (see picture): Your pool's long diameter is 25 ft, Short diameter is 15 ft and the pool's average depth is (3 + 7) / 2 = 5 ft. Pool's capacity is 25 x 15 x 5 x 5.9 = 11,063 gallons. Go to Step 5

Step 4
kidney swimming pool

KIDNEY SWIMMING POOL - To determine the number of gallons of water in your kidney pool, measure the largest width, the smallest width and the average depth. Average depth is determined by adding the depth at the shallow end to the depth at the deep end and dividing by 2. The formula for calculating total gallons in an kidney pool is: Gallons = (Longest width + Shortest width) x Length x Average depth x 3.38. 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. 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 8 hours. To come up with this flow rate simply divide your calculated gallons by 8. 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. A good estimate is to take the average amount of feet from where your suction lines are (skimmers or main drain) back to where your pool pump will be located. The picture at the right provides an example of how the average Feet of Head would be calculated for a pool with 3 suction returns, two skimmers and one main drain. The lengths of each line are: Skimmer 1 - 5'+15'+25'+15'+10' = 70'; Skimmer 2 - 15'+10' = 25'; and Main Drain - 25'+20' = 45'. To get the average Feet of Head take the three suction line lenghts and divide by three. 70' + 25' + 45' = 140' / 3 = 47 Average Feet of Head

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 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 calculated above for a typical RECTANGULAR pool, we are looking for a pump that will handle 42 GPM 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 to 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, Harward 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 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 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: fountains, spas, waterfalls, solar heating, and infloor cleaning systems. The features generally require higher GFM rates which equates to a higher HP pumps. Also if your pool requires greater than 60 GFM 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.

Comments (1 to 40 of 173)

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User: Inyopools

Madche – I would go with a 1.5 VS pump. You will see a considerable savings in operational costs even with your smaller pool. See our guide on “How to Save Money Using a Variable Speed Motor” for more information.

User: Madche

It is an in ground pool.
Thanks for any advice

User: Madche

I have 10,000 gallon pool with some spa features, a fountain and solar heating on the roof.
The Hayward Northstar pump motor died. It was 2hp, 1.1sf. What size replacement do you recommend?
Single, dual variable speed. I understand that variable is most economical in the long run but someone told me for my small pool it won't matter.

User: Inyopools

t-lu - 30,000 is a lot of water to filter but since you only have two lines into the pump (skimmer and dedicated suction) and two return lines, your GPM flow is somewhat limited. A 1.5 HP motor is a good choice. You might also consider a 2 speed or variable speed pump for a large saving in operational costs.

User: t-lu

hi, I have a little more than 30,000gallon inground, I have one skimmer, 2 return lines and a dedicated line for a Polaris 360, all lines I had upgraded to 2". I use a jandy valve to control water flow to Polaris and jets. my pump just went out, my question is what size pump should I replace with, im thinking a 1.5hp. I generally run 24hrs a day in summer

User: Inyopools

tdeist - For your size pool and based on the size of your old pump, I would recommend one of the smaller VS pump like the Hayward Max-Flo 1.5 HP Variable Speed Pump. The larger VS pumps would be overkill. For a DE filter I would recommend something like the Hayward Pro Grid DE Filter 60 Sq Ft. This is a step larger than what you need but most people buy a larger size to extend the maintenance period. You will also need to buy the multiport valve that goes with this filter - Vari-Flo Valve 2" for DE.

User: tdeist

16x34 foot rectangular pool, average depth of 4', about 17,000 gallons. Existing pump is a pacfab challenger 1 1/2 hp, pump motor is a centurion 1 1/2 hp. existing filter is a hayward c1750 single cartridge filter. seems i am constantly having to clean the filter! I want to upgrade the existing pump and filter. would be interested in purchasing a variable speed pump. I want to upgrade the filter to a DE filter. what do you recommend for both the pump and the filter? thanks!!

User: Inyopools

Ellen - Hayward is one of our best manufacturers. They sell this set that would meet your stated requirements - Hayward Super Pump 1 HP Single Speed W/ S244T 24" Sand Filter & Valve.

User: Inyopools

Archtec - Sorry for the late response. I would go with the smaller VS pump for your size pool. You can adjust the speed for exactly what you need for the salt system. Pump companies built the smaller pumps to handle these smaller pools. The larger VS pumps are overkill.

User: Ellen

Hello, I have an 18,000 gal pool and the filter and now pump need to be replaced. There is currently 2" piping and I am loooking into a 24" filter with 1 HP pump. Is there a brand you recommend? The pool is considered a play pool and is 5' deep max with 2 returns, 1 skimmer & 1 drain, the filter/pump is about 2' away from the pool. thank you

User: Archtec

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

User: Inyopools

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.


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

User: Inyopools

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.

User: Stevo

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

User: Inyopools

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

User: Chris

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.

User: Inyopools

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).

User: Dynakat

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.

User: Inyopools

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.

User: jwsp

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.


User: Inyopools

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.

User: Anthony Dal

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

User: Inyopools

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.

User: Sarah

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!

User: Inyopools

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.

User: Inyopools

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.

User: Damon

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

User: nancy

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.

User: Inyopools

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.

User: Damon

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

User: Inyopools

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.

User: CCWP

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?

User: Inyopools

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.

User: DASMan

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

User: Inyopools

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.

User: DASMan

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.

User: Inyopools

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

User: Inyopools

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.

User: Ccbcr2000

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.

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