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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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InyoPools Product Specialist  Posted: 6/14/2015 

jb - I assume when you say "on the ground pool", you mean above ground and not in-ground. It makes a difference. For a 1HP above ground pump I would recommend a Hayward Matrix Pool Pump 1 HP.
 Reply

 Posted: 6/14/2015 

I have a 17,000 gallon pool, the skimmer and drain lines are a total of around 60 ft (30 feet head?). I am estimating here since I wasn't around when the pool was built. It's 1.5 diameter pipe. I currently have a Hayward Perflex (340G34) that was installed a few years ago to replace the older one. The motor is shutting off every 30 mins or so to cool down. I think the bearings are probably shot. What size Super Pump should I get to replace the old one?
 Reply

 Posted: 6/11/2015 

I have a 16 x 32 on the ground pool, I need a new pump with filter basket, my pump was a 1 hp class cx 230/115 volt 6/12 amp 3450 rpm, what would you recommend, I have an established account with you,
 Reply

InyoPools Product Specialist  Posted: 6/2/2015 

Len - I would recommend Hayward Star Clear Cartridge Filter 50 Sq Ft for a cartridge filter. It would be compatible with either a new SP1750 pump or a converted SP2605x7 pump with a 1/2 HP impeller. See our guide on "How To Downsize a Pool Pump Impeller". If you stay with the existing 3/4 HP pump, I would recommend a larger filter like Hayward Star Clear Plus 75 Sq Ft. Filter 1 1/2" Ports.
 Reply

 Posted: 6/2/2015 

(follow up)

After some internet research, I might be able to downsize my impeller to 1/2 HP. Is this correct? will this alleviate my problem? I'm afraid it still might overpower my small sand filter. If I switch to cartridge, what Cartridge filter would you recommend with the 1/2 hp impeller?


Bought a house with a pool. mixmatch equipment Pac-Fab tagelus TA-30D sand filter and a Hayward sp2605x7 pump. The pool is a older pacific pools in ground 19 foot round. est about 8500 gal. I think the pump is overpowering the filter. Bigger filter or smaller pump. Thinking SP1750 pump and maybe switch to a cartridge filter. Recommendations? Equipment is less than 20ft from the pool single skimmer and single return.
 Reply

 Posted: 6/1/2015 

Bought a house with a pool. mixmatch equipment Pac-Fab tagelus TA-30D sand filter and a Hayward sp2605x7 pump. The pool is a older pacific pools in ground 19 foot round. est about 8500 gal. I think the pump is overpowering the filter. Bigger filter or smaller pump. Thinking SP1750 pump and maybe switch to a cartridge filter. Recommendations? Equipment is less than 20ft from the pool single skimmer and single return.
 Reply

InyoPools Product Specialist  Posted: 6/1/2015 

what size? - Sounds like the old shaft seal may have leaked and sprayed the motor bearings and damaged them. Generally when the motor starts making a load noise, owners have to replace the motor. We generally recommend a 1 1/2 HP motor for a 30" round AG pool but that's with a flat bottom. Depending on your pool's average depth, you may need something bigger and since your pool was originally fitted with a 2 HP motor, I would stay with that.
 Reply

InyoPools Product Specialist  Posted: 6/1/2015 

Allan - For your size pool and with 2" piping, the 1.5 HP Pentair Superflo VS would be a good selection for you.
 Reply

 Posted: 5/31/2015 

I have a 30' round above ground pool with deep end. We recently changed out the shaft seal. When we put everything back together the motor/pump was making loud humming noises. Should I replace the motor or motor/pump? What size? It currently has a 2hp motor.
It appears to be running great just sounds much louder
 Reply

 Posted: 5/30/2015 

Looking for a new 230v variable speed pump. I have an in ground with about 21,500 gal. All 2" PVC. 2 skimmers, 3 jets, main drain, and a 1/4" stream coming out of a small fish sculpture. Pump is 45' from near end of the pool, so I estimated an average head of 89' to the skimmers and drain. Failed pump was Pentair Challenger II, total HP 1.65. 24" Triton II sand filter rated at 60 gpm. I want to go with a VS pump. I've looked at Pentair Superflo VS (and a Hayward equivalent) and Pentair Intelliflo 3HP. My instinct is the Superflo VS 1.5 might be sufficient. I noticed your previous comment that stepping up from 1.5 suction and discharge ports to 2" PVC will not affect performance. What pump do you recommend? Thank you.
 Reply

InyoPools Product Specialist  Posted: 5/30/2015 

Chikkita - With a 20,000 gallon pool, you are on the edge of what we recommend for a 1.5 HP or 2 HP pump. I would go with the 1.5 HP pump for lower operating costs.
 Reply

InyoPools Product Specialist  Posted: 5/30/2015 

jenna13 - Yes. You can replace the motor of your super pump with a Century 2Green Motor using the same wires currently going to your super pump motor. The switching capability is incorporated in the motor. See our guide on "How to Replace a Single Speed Motor with a 2Green Motor" for more information. Other 2 speed options generally require 3 wires plus ground and another timer.
 Reply

 Posted: 5/28/2015 

I have a 20x40 inground, 33000 gal, with 1.5 inch plumbing. Skimmer and a bottom intake.
Filter is a Hayward 4820 48sqft max rate 96 gpm.
I calculate an average dynamic feet per head of somewhere around 30 fph this is a 30ft skimmer run.. level ground and the bottom - 8ft rise and 12 feet away from pump.
The issue is, the DE filter pressure is always 30 psi. If you use one intake it's 20. (Yes I clean my filter grids way more than the average person.)
There is a bunch of twists and turns on the pressure side because of a heater.
Is the 1.5 drawing in too much water for this system? Should I go to a 1hp Hayward Maxflo??
Thanks so much .. pulling my hair out :-)
 Reply

 Posted: 5/27/2015 

I am about to construct a lapping pool with the following dimensions 25 meters x 2.5 meters , 4 feet depth. My contractor suggests a 1.5 Hp pump. Another suggests a 2 Hp. What can you suggest and what other information might you need to make a sound recommendation? Thanks
 Reply

 Posted: 5/27/2015 

My 1hp superpump is dead. Can I get a two-speed pump in it's place w/o changing all of the electrical requirements?
 Reply

InyoPools Product Specialist  Posted: 5/25/2015 

Chaskinsnc - We generally recommend a 1 1/2 Hp pump for your size pool. I would recommend a "Hayward Super Pump 1 1/2 HP Dual Speed" for your pool.
 Reply

 Posted: 5/23/2015 

I have a 26,730 gallon 18x36 rectangle roman ends end ground vinyl liner with 1 skimmer, 1 drain and 3 jets. GPH=3341, Feet to Head avg 70' 1 hp jacuzzi 2 speed pump with 22.5 sand filter. (Both discontinued) 12 seasons with ionizer system. I run on low 24 hrs and high when in use or cleaning.
I need to replace thE pump. What do you recommend?
 Reply

InyoPools Product Specialist  Posted: 5/21/2015 

jlew - First understand that you will need an in-ground pool pump for your pool. Above ground pumps are gravity fed since they are installed at the base of the pool. Your above ground pool has to be considered an in-ground since it is mostly below ground and the pump is installed almost at the surface of the pool. For your size pool I would recommend a 1.5 HP Hayward Super pump with a Hayward C17502 175 Sq. Ft. Cartridge Filter or with a Hayward S310T2 30" Sand Filter & Valve.
 Reply

 Posted: 5/19/2015 

Hello, I'm installing a 15k gallon above ground pool but am sinking the pool into ground with ~12" left above ground. It has one skimmer and one return. I want to run an auto vacuum from the skimmer and will be using a salt-water generator. The pump/filter will be hard plummed under ground for ~20ft and then back up out of the ground at the pump. I would like to know: (1) What size plumbing should I use? (2) Recommendation for pump and filter sizes for both sand and cartridge (I'm undecided on which). Thanks!
 Reply

InyoPools Product Specialist  Posted: 5/12/2015 

Patel - Assuming you have 1 1/2" piping, for your size pool, I would recommend a smaller VS pump like the "Hayward Super Pump VS Variable Speed Pump". For a cartridge filter I would recommend the "Star Clear Plus 120 Sq Ft. Filter 1.5" Ports"
 Reply

InyoPools Product Specialist  Posted: 5/12/2015 

helpplease - Hayward is one of our most popular brands for quality and price. You will probably have to do some minor cutting and gluing to fit the new pump into the system piping. See our guide on "How To Replace a Pool Pump With An Energy Efficient Pool Pump" for an example of what's involved in replacing a pump. Your other option is to just replace the motor on your pump. See our guide on "How To Replace the Motor on Your Pool Pump" for more information. And lastly, we have many guides related to pumps that you might want to review for general knowledge. Just click "How To Guides" at the top of the page and scroll down the MIDDLE list to Pool Pumps. Click on Pool Pumps to see list of pump guide topics. Start with "How a Pool Pump Works".
 Reply

 Posted: 5/12/2015 

Thanks for your help! Can you recommend a brand of pump? I'm really at a loss of knowledge here, husbands away. Just went to the pool store and I'm thinking Hayward again so we don't have to mess with different fittings?
Thanks again
 Reply

InyoPools Product Specialist  Posted: 5/12/2015 

helpplease - I would recommend a 1 HP full rated pump. Service Factor (SF) should be 1.3 or above. See our guide on "How To Understand True Pump Horsepower - Up Rated vs Full Rated" for further information on SF.
 Reply

 Posted: 5/11/2015 

It's actually model number C48l2n134c2 a.o Smith 1 HP pump with 115/230 volt that i need to replace.
Want to replace with Hayward pool system (pump+filter)
 Reply

 Posted: 5/11/2015 

I want to replace my A.O. Smith -ST1102 (1 HP; RPM 3450, 115/230 Volts,THP/SF: 1.5, AMP 18.6/9.3).

Can you suggest replacement for this pump (possibly dual speed or variable speed) and should i replace my sand filter with sand carthridge?? I am okay to spend little extra to save cost on operating.

I have rectangular pool - 10k gallon
 Reply

 Posted: 5/11/2015 

Hi. Pump just died after only 4 years. Pool is 12400 gallons. On skimmer, 2 jets probably 30 feet from pump, plus waterfall 15 feet from pump. What size do you think I need?
 Reply

InyoPools Product Specialist  Posted: 5/9/2015 

Terri For your size pool (~33,000 gallons) I would recommend one of the larger VS pump like: "Hayward EcoStar Variable Speed Pump W/ Lock Out" or "IntelliFlo Variable Speed".
 Reply

 Posted: 5/7/2015 

I have an inground 20x40 3ft-9ft pool. I'm thinking about changing to a vs pump. What size and kind do you recommend?
 Reply

InyoPools Product Specialist  Posted: 5/7/2015 

MCHILT - Yes, you can use a reducer on the discharge end of the VS pump change the 2" port to 1 1/2".
 Reply

 Posted: 5/7/2015 

I currently have Pentair Challenger 2HP. Is is plumbed with 2" inlet and 1-1/2 out. the 1-1/2 then goes to DE filter, heater and back to pool. The Pentair Intellipro VS has 2" ports for both intake and out. Can I use a reducer on the out flow to 1-1/2?
 Reply

InyoPools Product Specialist  Posted: 4/13/2015 

Duffiera - We use just the average distance from pool inlets to the pump, but this size calculation is a very basic estimate for a typical pool. A more thorough analysis involves factors like total length of piping, size of piping, number of fittings [turns in the piping], vertical heights [up to the solar panels] etc. For a more accurate analysis, you should have a pool designer look at it.
 Reply

 Posted: 4/10/2015 

When calculating Feet of Head is it only the distance from the skimmer to the pump? Or, is the return distance included? And, what about a solar heating system on a second story? That distance too?
 Reply

InyoPools Product Specialist  Posted: 4/10/2015 

phantom - Sounds like your spa is part of your main pool [return water to pool is a waterfall] so I question why it need a separate pump for the spa. Can't the spa be supplied water though the pool system like most pool systems. I don't understand your pool configuration enough to comment on a separate pumping system for the spa.
 Reply

InyoPools Product Specialist  Posted: 4/10/2015 

tmo - I would also recommend a 1 HP pump to match your smaller DE filter. You will just have to run it longer to filter all the water in your large pool each day. And a Pentair WhisperFlo is a good choice.
 Reply

InyoPools Product Specialist  Posted: 4/10/2015 

spmorin - You have a large pool, but since it is old, its piping is probably all 1 1/2" which restricts flow. I would suggest that your new pump be 1 1/2 HP or less to keep flow under 60 GPM. With a 1 1/12 HP pump you should have at least a 22" diameter Hayward sand filter. If your current filter is smaller than 22"and you don't want to replace it with a largter one, I would suggest a 1 HP pump. You will just have to run the system longer to filter all the water in your pool. Both will support your solar system.
 Reply

 Posted: 4/9/2015 

I have an 8 ft diameter in ground spa
3 ft deep. It has 1 bottom drain and return water to pool is a waterfall.
I have 30 ft to pump. Pump is 4 ft above
Spa water level or 7 ft above bottom drain. Little usage. DE filter.
Which pump do you suggest?
 Reply

 Posted: 4/7/2015 

28,000 gal, 1.5" lines, 2 skimmers, 2 drains, Pentair DE 36
Currently have a Hayward 1.5HP Superflo that is about ready to go. Local pool store recommended 1HP Pentair Whisperflo mainly due to filter size. I'd like to go as low as possible on the pump HP and run longer during the day.
 Reply

 Posted: 4/7/2015 

Our pump just died and we need to replace. Pool and most of the equipment is old.
Pool size is 18.5' x 36' average depth is 6'
One intake (skimmer) approximately 30' from pump and filter.
We also have solar panels on roof of house that water flows through after filter. Approximately 16' of 1 1/2 inch pipe up to roof, approximately 240 sq. ft' of solar panels on roof, back to pool is approximately 12' into what would normally be the outlet pipe form the filter.
Dead pump is Sta Rite Dyna Glas MPRA6E-147L
Filter is Hayward sand filter, unsure of size.

thanks,
 Reply

InyoPools Product Specialist  Posted: 4/6/2015 

Clemsongirl - For your size pool customers typical buy a 1 1/2 HP pump and a 120 sq ft or 175 sq ft cartridge filter. I would recommend something like a Hayward Super II EE 1 1/2 HP Pump and a Hayward Star Clear Plus Cartridge filter: C12002 or C17502. The larger filter will last longer and require less frequent cleaning. For greater operational savings I would recommend a two speed pump (25% savings) or a smaller variable speed pump (50% to 75% savings).
 Reply

 Posted: 4/5/2015 

20'x40' Rectangle 2' Radius

3'4" Shallow Depth, 8' Deep Depth
What size pump/model do you recommend?
Perimeter 116'-7""

Gallons 27900

One skimmer, Pentair salt system, 4-5 feet from pool to pump
 Reply