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Swimming Pool Calculations

When purchasing a new swimming pool or swimming pool product there are several calculations that can be helpful. Below are a few calculations that may help determine the size of your swimming pool, heater, filter, or many other products. Please select from the following calculations...

 

Surface Area
The surface area of a swimming pool can help determine the BTU size of pool heaters.

Pool Shape
Formula

Rectangular
Surface Area = L X W

Round
Surface Area = 3.14 X (D/2) x (D/2)

Kidney
Surface Area = .45 X (A + B) L

Gallons of Water
Determining the gallons of water in your swimming pool can help determine such thing as the size of your pump and filter. The gallons of water depends on the shape of your pool.

Gallons of Water calculator

aD = Average Depth
Pool Shape
Formula

Rectangular
Gallons = Length x Width x Average Depth x 7.5

Round
Gallons = Diameter x Diameter x Average Depth x 5.9

Oval
Gallons = Long Diameter x Short Diameter x Average depth x 5.9


The Horse Power of Inground Pool Pumps

The three best manufacturers of pool pumps are Hayward, Pentair, and Sta-Rite. Each manufacturer sells different models of pumps. These models range in performance, and are rated by their Horse Power (HP). There are two important factors when trying to figure out which HP pump, the gallons per minute (GPM) and the Amount of head in feet. In order to figure out what ideal GPM you need for your pool pump follow these steps.

  • To figure out the amount of gallons in your pool use this calculator
  • A good rule of thumb is you should be able to clear your swimming pool in an 8 hour period of time. Take the number of gallons and divide that by 8.

Ideal Gallons Per Hour (GPH) = Gallons of pool water / 8

  • Next take the GPH and divide that by 60
Ideal GPM = GPH / 60

Now that you have the ideal GPM you need to figure out the Feet of head of your pump. A good estimate is to take the amount of feet from where your suction lines are (skimmers or main drain) back to where your pump will be located. The total amount of return piping should give you a good idea on how many feet of head your pump will have.

Many of the Swimming pool pumps will have charts showing the Horse Power of each pump. These charts are usually shown with the GPM vs. The Feet of Head.

For example, if you have a 20,000 Gallon pool.

GPH = 20,000 / 8 = 2,500

GPM = 2,500 / 60 = 41.7

Now that you have your GPM, we need to make a couple more assumptions. Let's say you choose the popular Hayward Super Pump and you have found your total return piping to be a total of 30 feet. N ext look at the chart listed on Hayward Super pump description page (see below)

Click here for the Hayward Super Pump description page

 

Pump Output (GPM) vs. Total Resistance To Flow (Feet of Head)

Model No. Max Rated

20 ft

30 ft

40 ft

50 ft

60 ft

70 ft

SP2600X5

55

45

29

--

--

--

SP2605X7

67

58

47

31

--

--

SP2607X10

85

76

65

50

27

--

SP2610X15

97

90

80

67

50

10

SP2615X20

116

111

99

85

70

51

SP2621X25

109

109

104

95

84

69

With 30 feet of head and 46.7 GPH we would use the SP2605X7 (always go to the higher size GPH, 58 in the example). The SP2605X7 is a 3/4 HP pump.


The Size of Inground Filters

The most important factor of the size of the Swimming Pool Filter is the GPM your Pool Pump produces. Filters have a designed flow rate. This designed flow rate should be higher than the size of your GPM your pool pump produces.

In the example above we were using the Hayward Super pump that produces a 58 GPM at 30 feet of Head. If we were to choose the Hayward Star Clear Plus as our choosen filter we would use the chart found on the desription page
Click here for the Star Clear Plus description page.

Performance Data--Residential

  Turnover (In Gallons)
Model Number Effective Filtration Area Design Flow Rate* 8 Hours 10 Hours
C7512 75 ft2 75 GPM 36,000 45,000
C9002 90 ft2 90 GPM 43,200 54,000
C12002 120 ft2 120 GPM 57,600 72,000
C17502 175 ft2 120 GPM 57,600 72,000

The size of the filter that could handle the 58 GPM Super Pump would be the C7512.


The Size of the Above Ground Pump and Filter System

The size of your system is mostly determined on the size of your above ground pool. The gallons found inside your pool will give you the horse power needed for your pump. A simple rule to follow is you should be able to clear all of the gallons of your pool in an 8 hour period of time. You can use the following as a guideline.

• Above Ground Pool up to 24 Ft. Round = 1 HP pump
• Above Ground Pool over 24 Ft. Round = 1 ½ HP pump


Determine the BTU Size for Swimming Pool Heaters

The Surface area will help determine the BTU size of your pool heater. Decide on the temperature rise you want per hour Then consult this chart. Heat rise will vary slightly when dealing with different heaters. We usually recommend an increase of 1 - 1 1/2 degree per hour.
Pool Size -Square Feet
BTU Size
500 Sq. Ft.
650 Sq. Ft
800 Sq. Ft.
200
1 degree
1
-
250
1 1/2
1 1/2
-
350
2
1 3/4
1
400
2 1/2
2
1 1/4