In order to figure out the proper doses of chemicals for your pool, you need to determine how many gallons of water it holds. To do that, you need to use a ruler to measure your pool to find out these four different numbers; Length, Width, Average depth and a multiplier that determines gallons.

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So here are the formulas to figure out how much water is in your swimming pool:These formulas hold true for both Inground pools as well as above ground pools.

Rectangular, Square or Free Form Pools:

Length x Width x Average Depth x 7.5 = Total gallons

For example: 16′ x 32′ x 4.5′ x 7.5 = 17,280 Gallons

Circular Pools:

Diameter x Diameter x Average Depth x 5.9 = Total gallons

For example: 18′ x 18′ x 4′ x 5.9 = 7,646 Gallons

Oval Pools:

Length x Width x Average Depth x 5.9 = Total gallons

For example: 15′ x 30′ x 4′ x 5.9 = 10,620 Gallons

How to determine the Average Depth of a Swimming Pool where the bottom slopes:

Below is a side-shot of the “typical” inground pool that has a shallow end (see “D”), then a slope that leads into the deep end (see “C”).


First measure the depth of “D”, the shallow end (usually anywhere from 3′ to 5′), and then measure the depth of “C”, the deep end (usually anywhere between 6′ and 12′) . Then, add them together and divide by 2. This is the average depth of your pool.

For example, if your shallow end “D” is 3′, and your deep end “C” is 8′, this would be your formula for the Average Depth:

3′ + 8′ = 11′

11′ divided by 2 = 5.5.

Therefore, in this example, your average depth would be 5 1/2 feet.

Most Common Sizes Of Inground Rectangular Pools

Below, we have created some handy charts of the most popular sizes of poolsand how many gallons of water are in them.

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12′ X 24′8,6409,72010,80011,88012,960
14′ X 28′11,76013,23014,70016,17017,640
15′ X 30′13,50015,20019,90018,60020,250
16′ X 32′15,40017,30019,20021,10023,040
18′ X 36′19,40021,90024,30026,70029,160
20′ X 40′24,00027,00030,00033,00036,000
25′ X 45′33,75037,96842,18746,40650,625
25′ X 50′37,50042,20046,90051,60056,250
30′ X 50′45,00050,52556,25061,87567,500

Most Common Sizes Of Above Ground Pools


Above Ground Pools with a Depth of 48″ (4′)



12′ Round3,398
15′ Round5,310
18′ Round7,646
21′ Round10,407
24′ Round13,593
27′ Round17,204
28′ Round18,502
30′ Round21,240
33′ Round25,700
15′ x 30′ Oval10,620



12′ Round3,823
15′ Round5,973
18′ Round8,602
21′ Round11,708
24′ Round15,292
27′ Round19,354
28′ Round20,815
30′ Round23,895
33′ Round28,912
15′ x 30′ Oval11,947

More Detailed Information For You:

If you are not using a cell phone, and are using a desktop computer, laptop or tablet, we do have a very detailed page with more information PLUS an online Pool Water Calculator on our Classic Pool And Spa desktop site.Click here to see our E-Z Pool Water Calculator page.

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