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# How many gallons of water are in a 4'x18' pool and what is the formula for figuring it out?

Wiki User

2015-07-16 19:28:48

For a round above ground pool, the calculation is:

Diameter x Diameter x Depth X 5.9 = Number of Gallons

Edit note : The above formula uses the conversion factor of 5.9 US gallons to the cu. ft.

From my high school days, a century ago, I believe this is incorrect.

I recall that 7.48 US gallons occupy one cu.ft. of water. I checked my memory of this at two different websites which confirmed my recollection.

The second site is [ http://www.math.com/students/converters/source/volume.htm ].

Thus the answer given below appears to be approx. 25 % too low.

Perhaps the 5.9 incorrectly used above, is the British or Imperial gallon conversion factor ?

Please note that the depth is the ACTUAL water depth NOT the height of the pool wall (the water is usually around 6 inches lower than the wall height).

For a 18-foot round pool with an actual water depth of 3.5 ft: 18x18x3.5x5.9 = 6,690 gallons. NOT CORRECT !!!

Corrected answer : 18 x18 x3.5 x 7.48 = 8,482 US gallons

Visit this page: http://www.poolspa.com/calculator/ which uses the correct 7.48 conversion factor for US gallons

Depends on the shape of your pool.

Round or Oval pools:

Length * Width * Average Depth * 5.9 = Gallons

Rectangle, square, or free-form pools:

Length * Width * Average Depth * 7.5 = Gallons

Wiki User

2015-07-16 19:28:48
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