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 by Step


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.


(321 to 360 of 603)

 Posted: 3/1/2016 

We have a 10,000 gal. pool with a spa. Recently, we switched from a single 1 1/2 THP speed pool pump to a variable 1 1/2 THP speed pool pump. The water seems to filter fine at 2000 rpms. However, our vacuum cleaner does not have enough suction at 3000 rpms to work efficiently as it did with the single speed pump. Also, our spa feature is not working. Do we we need a larger pump?

InyoPools Product Specialist  Posted: 2/23/2016 

mvcain - If you go with the larger 3 HP VS pump, I would recommend upgrading your Tagelus 60 to a Tagelus 100. We always recommend sizing your filter to the next level to have a buffer in filter capability. And you won't have to backwash as frequently.

InyoPools Product Specialist  Posted: 2/23/2016 

mvcain - A 3 HP VS pump would not hurt your system. Because it is a VS pump, you have the flexibility of running just the speed (HP) you need to meet you pools system needs. The larger pump is probably more than you need currently, but a 1.5 pump is on the edge of meeting your current pool requirements and the larger pump would give you the option to add other features onto your system later. If you choose the larger VS pump, the Intelliflo pump is a popular choice.

 Posted: 2/23/2016 

The current sand filter I have is a Tagelus 60. Not sure if that would need to be upgraded to accommodate the larger pump. thanks!

 Posted: 2/22/2016 

Hello, I am looking to replace my 1.5hp Pentair single speed pump with a Pentair variable speed pump. My pool is 19,300 gallons, with 65 feet of pump head. I have a slide and 3 deck jets. Would a 3hp model be harmful? I have 2 inch pipes and a relatively large sand filter. I was looking at the Intelliflo Variable speed pump (011018). Any suggestions? Thanks!

InyoPools Product Specialist  Posted: 2/15/2016 

Diana - Hayward just came out with the Hayward Super Pump VS Variable Speed Pump (115V). It is the only VS pump I know of that uses 115V. It has .85 Total HP.

InyoPools Product Specialist  Posted: 2/15/2016 

CTRICH - For your size pool, I would recommend a 1.5HP pump with a larger sand filter - like the Hayward Super Pump 1.5 HP SINGLE Speed W/ S310T2 30" Sand Filter & Valve. If you are going to the effort of digging around the pool, I would definitely replace the 1.5" pipes with 2" pipes. The 1.5 pipes are borderline for the flow you need. And I'm not sure why you are elimination the deep end drain. You will have to run a suction or robotic cleaner longer to clear the bottom debris and circulate the bottom water.

 Posted: 2/14/2016 

My pool is 18x36 inground with 8ft deep end. (26,730gal). would like to turn over in 8hrs. (56-60gpm). Looking for new Hayward sand filter and pump. Digging up around pool in spring and eliminating deep end drain. Only suction will be skimmer. Should I convert from 1.5" pvc on suction line to 2"? I also have a heater with min flow of 57gpm and max 70gpm. What size filter and pump should I get? currently have old S220T and 1 HP Superpump. Thinking of S244T with 1hp?

 Posted: 2/12/2016 

We need to replace our pool pump. We only have 110 volt at the pump house. I'd like to go with a variable speed our gpm 42.2 and I think we need a 1.5 horse power pump. What do you rec2.
Thank you


InyoPools Product Specialist  Posted: 1/19/2016 

Mujahid - Your pool will hold approximately 16,000 gallons of water. For that size we would recommend a 1 1/2 HP pump with a 30" sand filter like the Hayward Super Pump 1.5 HP SINGLE Speed W/ S310T2 30" Sand Filter & Valve.

 Posted: 1/19/2016 

I am going to construct a new indoor skimmer swimming pool in rectangular shape,
Pool size: 9m * 4.5m
Pool depth: 0.95m to 1.75m
Total volume: 60.75m3 (Approximately)

Can you please help me out that which size of sand filter I can install and how many HP it can be?

Thank you


InyoPools Product Specialist  Posted: 1/13/2016 

david - I would recommend a set like the "Hayward Super Pump 1 HP Single Speed W/ S244T 24" Sand Filter & Valve" or comparable.

 Posted: 1/13/2016 

i have apool 13500 gallons, its head is about 55ft,the pumpbeing at the opp end from skimmer box and pump is about 6 ft below top of pool

what size pump and sand filter should i get?



InyoPools Product Specialist  Posted: 12/11/2015 

radus - If I have the numbers right, you have a 32,400 gallons pool which is comparable to the one we discuss in a guide on "How To Set Up In Ground Pool Equipment - Part 0 - Overview. It goes into detail on what equipment to consider for installing a large 30,000 gallon pool including discussions on circulation, water features, heaters, automatic chemical feeders, lighting, and control systems. In general terms this pool system has one pump and filter for circulation and a second pump and filter for the several water features. If your pool system does not have extensive water features, you could probably get by with one pump and filter. See our guide for details.

 Posted: 12/9/2015 

I have a new in-ground pool 12'x72'x5'(depth). In a long side there are 4 skimmers, in the other 8 returns and 2 drains; everything built in 2" pipes.
Now is time to build the plumbing; some pool professionals give me 2 options:
- 1 pump, 1 filter and 1 electric heater
- 2 pumps, 2 filters, 2 heaters
Other professionals give me combinations between those two.
What's your opinion? And how many HP for the pump(s)?


InyoPools Product Specialist  Posted: 10/21/2015 

Gayle - If your pool was originally configured for a 1 1/2 HP pump, a 3/4 HP pump may not be big enough to overcome the resistance in your pool's piping system (feet of head). A 3/4 HP pump is operationally not the same as a 1 1/2 VS pump running at half speed. When a VS pump drops to half speed, it reduces flow which cuts the resistance in half. It also cuts the amperage to an eighth of the amperage at full speed. The VS pump would be the way to go to save energy.

 Posted: 10/20/2015 

We need to replace our old pool pump. Our previous pump was a Pentair 1 1/2 hp. My husband wants to replace it with a 3/4 hp saying he will run it longer but will save us money because it uses less amps to run. I think buying a variable speed would be better, what would you suggest? Thanks!

InyoPools Product Specialist  Posted: 10/12/2015 

pump replacement - The Pentair Challenger 2 HP 230V FR Pump would be a good replacement for your old Pac-Fab Challenger pump.

Anonymous  Posted: 10/12/2015 

I am trying to determine what pump might be a good selection. I am replacing a 20 yr old Pac-Fab Challenger pump. Label on the side of the motor says Century Centurian and A. O. Smith. I cannot find a model number on the pump itself

CAT: B855
PART: 7-177897-22
HP: 2.0 SF 1.10 PH 1
HZ: 60 RPM 3450
VOLTS: 230
AMPS: SF 10.0
CODE: P (or might be F) INSUL CLASS: B AMB: 50 ºC

The pool, including spa, holds 30,000 gallons.
If my calculations are close, I am looking at about 35 feet of head.
Piping is 2”
Filter 60’ Nautilus Steel DE filter
Polaris 360 & booster pump


InyoPools Product Specialist  Posted: 9/16/2015 

SteveP - There are two sizes of VS pumps on the market currently: 1 1/2 HP and 3 HP. For your size pool and pool features, I would recommend a 1 ½ HP VS pump. If you are partial to Pentair, here is a link to their Pentair 1 ½ HP VS Super Flo Pump with Timer.

 Posted: 9/16/2015 

I am interested in replacing my Pentair 3/4 hp single speed pump with a VS pump but not sure what size or model I would need. My pool is just under 10,000 gallons. I have a gas heater and a separate dedicated pump for the Polaris. I see that there are few different models of VS pumps all with various features and benefits. So, I am trying to figure out which one I need and will it be strong enough to replace my two single speed pumps that are on my pool now.

InyoPools Product Specialist  Posted: 9/13/2015 

Dave - For your size pool and stated features, we would recommend the 1.5 HP Pentair VS SuperFlo Pump. California does require a 2-speed or VS pump to conserve energy. The VS pump does cost a little more initially but you will recoup that cost in operational energy savings in a little more than a year. Pentair also offers a 3 HP VS pump but that would be overkill for you pool setup.

 Posted: 9/12/2015 

Hi guys, I need some help selecting a new pump. The pools old, about 25 years old and this may be the original pump. From the stickers looks like it's a Challenger Pac-Fab 2hp and on motor says Centurian for Pac-Fab. Service factor is blank, amps= SF 9.6-8.8, rpm= 3450. If my calculations are correct the pool is about 14,500 gallons, including spa with 16-18 feet of head (hopefully this is close). 2 inch piping with new Pentair clean/clear plus 420 cartridge filter. Has Polaris 360 sweep with Jandy valve for flow, water fall, on roof solar heating and I already mentioned the spa. I want a Pentair pump and was looking at 1.5 or 2 hp single speed but live in California and read something about Title 20 restrictions for pool pumps. Would like to keep the cost somewhat under control. Recommendations would be much appreciated.

InyoPools Product Specialist  Posted: 8/26/2015 

Jrmags - I would have thought that normally the pump would be able to draw the water from a partially filled pool but you may be right. You may need the pressure of a fuller pool to help overcome the weight of a column of water going 65' up a 6' rise. Make sure you have no other suction pipes open or leaking.

 Posted: 8/26/2015 

We are currently installing an inground sports pool 40' x 18' with a 5.5' depth in the middle 1/3 of the pool. The pool has 42" depth on both shallow book ending the middle.

The water level is currently about 6 inches in each shallow end with the middle depth at about 2'.

At this point we wanted to test the main drains which has the 2 main drains tied together with single exit 1.5" pipe. The main drains are 65" away from the Hayward 1.5 hp super pump. It seems the pump is having a hard time pumping the water up the 65' @ a 6' rise in elevation.

The pump pumbling is tight, but the water seems to only make it 2/3 of the way to the pump then stalls with no water ever reaching the pump. We primed the pump by filling the basket and pipe, but a lot of the water drains into the pool from the pipe before we can start the pump. The basket is full and when the pump is turned on a portion of that water is expelled (the valve is set on Waste since no other suction or return lines are in use).

I'm thinking the pool water level may not be high enough to assist the pump in its effort to pump the water 65 feet @ 6' rise.

What do you think?

Tomorrow I will check the suction line for an air leak.


InyoPools Product Specialist  Posted: 8/17/2015 

GL Pool Services - Give one of our tech staff a call at 877-372-6038. They will be able to set up this order for you.

 Posted: 8/16/2015 

I need quote for quantity products is necessary for pool 160,000 gallons. When balance is.
Cloro 0
Ph 8.2
Alkaline 40
Acid cianuric 0


InyoPools Product Specialist  Posted: 7/31/2015 

Jeff R - Your 1 HP pump should be adequate for your size pool and other features especially with 2" piping. If your flow is good now, I would stay with the current size motor. If you increase the size of your pump, you will probably also have to increase the size of your filter to match the GPM flow rate of the larger pump.

 Posted: 7/30/2015 

I have a 9,500 gallon rectangular pool with 2" pipes for both skimmer and drain. I also have a 5 panel solar heater with 2" pipes, along with a 2" piped waterfall at the far end of the pool. I have a short Hayward cartridge filter (not sure of size). The current pump is 1 HP USQ1102. Should I replace pump with same model or increase my HP on account of the solar and waterfall?


Central Florida


InyoPools Product Specialist  Posted: 7/12/2015 

GreenPoolBlues - I would tend to agree with Craigz. Your 3/4 HP is probably too small to run your Serpent suction pool cleaner especially if your pump motor's Service Factor (SF) is 1.0. Depending on your system piping (1 ½’ or 2”) and the size of your pool, you should probably have a full rated 1.0HP or 1.5 HP pump to generate the GFM water flow required for this cleaner. Unfortunately, when you upgrade to this larger pump, you will also need to replace your filter to handle the higher GFM generated by the pump. I also agree with Craigz that your best option is to buy a Variable Speed (VS) pump. It will cost more initially but will pay for itself in a little less than a year in up to 80% less operational costs. And you will see significant savings after that year.

 Posted: 7/12/2015 

Greenpoolblues. Just a quick comment on your pump situation. I'm not to familiar with what your dealing with since I have a variable pump but I know when I set mine to .75hp it's not enough to do the suction vacuum. I've also read other online comments about how 3/4hp isn't really enough for some suction vacuums.
Someone correct me if I'm wrong but I think you should probably have a 2 speed 1.5hp so you have plenty of power for cleaning.
Personally tho I would go variable. Mine paid for itself in the first year.


 Posted: 7/10/2015 

I'm at my wit's end! Bought house last year. Pump threw a ball bearing so replaced it with 3/4 Pentair on reco of pool company to go with a Hayward Pro Series S210T sand filter (20 GPM filtration rate; 44 GPM filtration and backwash design flow rate). I've had a green pool ever since -- and my fear is that my filter is now undersized for the pump. Am I right? Recommendations? I also bought a Serpent pool vacuum (plugs into skimmer) but not getting enough suction to run the darn thing -- and think it's b/c of the wonky pump/filter balance. Stuck between rock and hard place. Any advice is VERY welcome and appreciated. Thank you.

InyoPools Product Specialist  Posted: 7/2/2015 

Frankie - Yes that combination will work for your size pool.

 Posted: 7/1/2015 

Hi, so I have a 28,000 gallon pool with a sta-rite 2hp motor and a tr100 sand filter all 2"plumbed with a multiport valve. Is this going to work?

InyoPools Product Specialist  Posted: 6/26/2015 

Shin - Your pump and filter have to be matched to work properly. If your pump is pushing around 70 GPM and your filter is designed for 32 GPM, your filter is way too small for your system. We generally recommend that you get a filter one size larger that required [over 70 GPM] so you are sure it will handle whatever the pump generates. It's all right to have a filter larger than needed but it can't be smaller.

 Posted: 6/24/2015 

I am having a problem and hoping someone here could give me a bit of advice or at least where to look for the correct answer:

Im a fairly new Pool owner and I have an Above ground pool: it is 22X12 (oval) with 4 feet of max depth (all around: 48 inches deep).

I bought a Hayward Motor which is 1.5 HP (according to the tag) that pushes 70 GPM (again according to tag) and a DE Fliter system that handles 32GPM. This is what was recommended to me by the pool company.

So my issue is this: I set everything up the hoses are all snugly on and I even changed the hoses because I figured this was the problem, When the pump gets going the pressure gauge slows 15PSI and the flow of water is very strong: the pump is flowing and all is normal: but within 10/30 mins (more often average of 15 mins) The gauge climbs to 20PSI and the flow of water pumping decreases GREATLY (from strong flow to a whispering push) And soon enough the water flow stops all together or is moving so slow that I think it stopped. The motor makes a whining grind sound (sometimes) when this happens.

So I clean it out, traps and all and turn it back on: repeats starts strong and within that time span the same results happen: No water flow or very slow water flow. I checked if there was air trapped and didn't appear to be any air leaking, or flow, hoses changed, and tightly on, Everything appears normal and connected correctly but I still lose the pressure.

I assume and, this is where I can't find an answer that the Pump is to strong for the fliteR? Again the 1.5 pushes 70 GPM and the filter says it can do 32GPMm, do I need a weaker motor? Or a bigger filter? or is my issue something completely unrelated?

Again check list:
Water is filled well above water line.
Hoses where changed and tightened
Filter was cleaned
No air present (that i see)
Filter traps cleaned, checked for clogs.

Any help on this subject would


InyoPools Product Specialist  Posted: 6/23/2015 

frank - For your size pool you might have gone to a 2 HP pump but your 1 1/2" piping restricts you to a max GPM flow rate of around 60. So you are probably good with you 1 1/2 HP pump.

 Posted: 6/23/2015 

My pool is rectangular, 20x40 about 33,000 gallons, with about 45 feet of head avg. 1 1/2 in pipe, 22 in hayward sand filter, I just ordered the Hayward super pump 1 1/2 hp sp2610x15 Is this a OK set up? I cant tell what my old pump is because the label is too faded(old century).

 Posted: 6/19/2015 

I would like to replace a 25-year-old 1 HP Hayward pump. I have 15x30 inground pool with 2 inch pvc plumbing. Which Hayward model would you recommend.

InyoPools Product Specialist  Posted: 6/14/2015 

nmax - You would want to match the new pump size to the size of your current filter. I cannot tell from your filter id number [340G34] which size filter you have. It doesn't come up in our system or the internet. Without the filter size, I would have to recommend that your replace the old pump with a motor that is the same size assuming they were matched correctly originally.