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.

(361 to 400 of 542)

Posted: 1/13/2015

I have a 15,000 gallon (~800 Sq. ft. surface area) in-ground pool with 2 return lines, 1 skimmer and 1 dedicated vacuum port. Max, 20' of head. My Vacuum is the Baracuda G3 Residential Advanced Suction Side Automatic Pool Cleaner. Need to replace pump with a Variable speed pump to get an SCE rebate. What would you recommend? Also need to replace by DE filter, Would like to stay with DE. What would you recommend?. Would also like to add a heater. Max 25 degree temperature rise Gas line is already in place. What would you recommend. Thanks

InyoPools Product Specialist  Posted: 1/13/2015

Justin - For your size pool, I would recommend a 3/4 HP pump with a Uprated motor (Service Factor (SF) of less than 1.15 - like this Hayward 3/4 HP Super Pump. Note: I am assuming this is a small in-ground pool. If it is above ground, you will need an above ground pump.

Posted: 1/12/2015

I'm looking to replace an overkill 2HP Pentair Whisperflo WFE-8 on my 8,000 gallon pool with 1 skimmer and 1 drain with an average 13 feet of head all returning through magnasweeps. What would you recommend?

InyoPools Product Specialist  Posted: 1/9/2015

Jc - For your size pool and its associated operational costs, I would recommend getting a large 3 HP Variable Speed (VS) pump. That way you could run it most of the time at a lower speed to circulated the water and then run it at full speed when you want to use the spa. It will save you up to 75% on operational costs over using a single speed 2 HP pump. See our guide on "How to Save Money Using a Variable Speed Motor" for more information. This VS pump would take care of all the features you listed. You would not need an additional pump.

Posted: 1/8/2015

I am building a very large pool 60x25 with spa 15x7, cascade and slide. I figured around 56,175 gallons of water with ur calculations. Do i need a 2hp motor? And if so seperate motors for spa and cascade?

InyoPools Product Specialist  Posted: 12/30/2014

S2BEIT - I would recommend a 1 HP above ground pump for your setup. Two factors to consider when replacing your pump: Total Horse Power (THP) and type of pump. The actual or THP of a pump is determined by multiplying its HP by its Service Factor (SF) - both stated on the label on the pump's motor. The Hayward PowerFlo has a SF of 1.0 so your old pump's motor had a THP of 1.0 x 1.0 or 1.0 THP. The Pentair SuperFlo pump motors have a SF of 1.65 so for the 3/4 HP motor, its actual THP is .75 HP x 1.65 or 1.15 THP. The acutal THP of 1.0 HP motor is 1.0 x 1.65 or 1.65. In this case the 3/4 HP motor would have been the better match. However, factor two, the Pentair SuperFlo pumps are designed for inground pool which work through suction (pulling water to the pump). Your Hayward PowerFlo pump was designed for above ground pools and work off of gravity - pump is lower than the pool water surface and water drops into the pump. I would go back to the 1.0 HP Hayward PowerFLo or similar above ground pool pump.

Posted: 12/29/2014

HELLO,

I have an above ground pool 18x30oval around 46inch depth. What size pump do I need. My existing 1hp hayward Powerflo burned out. I was considering a 3/4 pentair supeflo or maybe 1 hp?

InyoPools Product Specialist  Posted: 12/21/2014

Capt Jack - I would go with a 1.5 VS pump for your size pool. 2 or 3 HP VS pumps sounds like overkill, especially with they have Service Factor (SF) of over 1.0. Total or real HP is the product of HP and SF. If a 2 HP pump has a SF of 1.5, your total HP (THP) is 3 HP. I would be looking for a VS pump of 1.5 to 2 THP.

Posted: 12/19/2014

HI, I have a 16,000 gal in-ground pool with 1 drain and 1 skimmer. Currently have a 1.5HP Challenger single speed pump that I want to switch to VS. This pump serves the cartridge filter (PacFab Seahorse 300 sq ft), pool cleaner (Polaris 360) and my roof top solar heaters. I have been getting varying HP recommendations locally (anywhere from 2 to 3 HP) and I am wondering what your thoughts are.

InyoPools Product Specialist  Posted: 12/15/2014

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.

Posted: 12/15/2014

It is an in ground pool.

Posted: 12/15/2014

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.

InyoPools Product Specialist  Posted: 12/1/2014

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.

Posted: 11/29/2014

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

InyoPools Product Specialist  Posted: 11/14/2014

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.

Posted: 11/12/2014

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!!

InyoPools Product Specialist  Posted: 11/4/2014

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.

InyoPools Product Specialist  Posted: 11/4/2014

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.

Posted: 11/1/2014

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

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

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.

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?

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.

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

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.

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.

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).

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.

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.

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

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.

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

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.

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!

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.

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.

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

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.

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.