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How To Calculate Pool Volume

Like a cook who needs to know how much of each ingredient to add to a dish, pool owners need to know how much of their maintenance products they need to add to their water. In order to do this properly, pool owners must know their pool volume — how much water is actually in their pool.

Calculating your pool volume is essential to correctly balancing the water. Making only rough estimates can result in errors and end up causing issues. Over-estimating is a waste of money; under-estimating will result in unsanitary water. If the volume of your pool isn't in the original documentation, it's easy to calculate it yourself.

Running The Numbers

Three average measurements are used to calculate pool volume for most pools: length, width, and depth. There are more complicated formulas for measuring oddly-shaped pools, but most of them also include these measurements.

If your pool has a shallow end and a deep end, you'll need to measure both in order to find the average depth. For example: The shallow end is 3' deep and the deep end is 8'. Using the Average Depth formula: (3+8)÷2=5.5' Average Depth.)

As you'll notice below, most of these formulas are multiplied by 7.5, which is approximately how many gallons are in a cubic foot. The pool size measurements will help you find the cubic footage of the pool, and multiplying this by 7.5 will help you find a close estimate of volume in gallons.

Once you have this number, you should be able to apply the correct amount of pool chemicals to your pool water and avoid any future dosage issues.

The combined formulas should look like this:

Square and Rectangle Pools:

Length x Width x Average Depth x 7.5 = Approximate Volume (Gallons)

Round Pools:

3.14 x Radius x Radius x Average Depth x 7.5 = Volume (Gallons)

The Radius equals the diameter divided by 2. (Example: A 16' diameter divided by 2 = 8' radius.)

Note: Most round pools have a single depth.

Oval Pools:

3.14 x Length x Width x .25 x Average Depth x 7.5 = Approximate Volume (Gallons)

Kidney-Shaped Pool:

(A + B) x Length x 0.45 x Average Depth x 7.5 = Approximate Volume (Gallons)

Note: “A” and “B” measurements are the two widest points of the kidney shape.

Irregular Shapes or Free-Form Pools:

Longest Length x Widest Width x Average Depth x 5.9 = Approximate Volume (Gallons)

Quick Reference

For your convenience, you can also consult the following charts. They detail the volume of many popular pool sizes.

Above Ground Pool Volume (48″ Wall Height)

Pool Size Gallons
15′ Round 5,300
18′ Round 7,600
20′ Round 9,400
24′ Round 13,600
27′ Round 17,200
28′ Round 18,500
11×25 Oval 6,500
11×30 Oval 7,800
15×25 Oval 8,900
15×30 Oval 10,600
18×33 Oval 14,000
18×38 Oval 16,100

Above Ground Pool Volume (52″ Wall Height)

Pool Size Gallons
15′ Round 5,800
18′ Round 8,300
20′ Round 10,200
24′ Round 15,300
27′ Round 18,600
28′ Round 20,000
11×25 Oval 7,000
11×30 Oval 8,400
15×25 Oval 9,600
15×30 Oval 11,500
18×33 Oval 15,200
18×38 Oval 17,500

In Ground Pool Volume (Standard Depth)

Pool Size Gallons
12×24 Rectangle 10,800
16×32 Rectangle 19,200
16×36 Rectangle 21,600
18×36 Rectangle 24,300
20×40 Rectangle 30,000
16×32 Oval 17,200
18×36 Oval 21,700
18×36 Oval 21,700
20×40 Oval 26,800
17×33 Grecian 19,700
17×37 Grecian 22,200
20×36 Grecian 24,300
20×44 Grecian 30,300
16×30 Kidney 14,900
16×34 Kidney 16,500
20×38 Kidney 20,200

For more information on pool size or chemical usage, check our complete blog library, or reach out to one of our knowledgeable staff members at your local Leslie's. At Leslie's, your pool is our passion.

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Leslie’s makes every effort to provide accurate recommendations based upon current ANSI/APSP/ICC-5 2011 (R2022) standards, but codes and regulations change, and Leslie’s assumes no liability for any omissions or errors in this article or the outcome of any project. You must always exercise reasonable caution, carefully read the label on all products, follow all product directions, follow any current codes and regulations that may apply, and consult with a licensed professional if in doubt about any procedures. Leslie’s assumes no legal responsibility for your reliance or interpretation of the data contained herein, and makes no representations or warranties of any kind concerning the quality, safety, or suitability of the information, whether express or implied, including, without limitation, any implied warranties of merchantability or fitness for a particular purpose.