Pool Volume Calculator

Pool Volume Calculator

It is important to know how many gallons of water are in your swimming pool for many reasons. This information helps with choosing the correct pool equipment, as well as the proper amount of pool chemicals to distribute in the water.

Round and rectangle pool shapes have simple formulas to calculate pool volume, while custom shapes require multiple calculations for an accurate reading. Below are the most commonly used formulas to easily calculate the amount of gallons in your pool.

If you just want an estimated pool volume, we also created a Pool Volume Chart at the bottom of this article. Click HERE to find your estimated pool volume in gallons.

Square and Rectangle Pool Volume Calculator

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

This calculation is for a swimming pool with a constant depth. For example, a pool that is 4 1/2 feet deep from end to end. Once you have the pool volume number, you can add the recommended amount of chemicals to your pool and avoid under or over-dosage.

Example: Your in ground pool is 12 Ft wide and 30 Ft long, with a depth of 4 Ft. The formula would look like this: 12 x 30 x 4 x 7.5 = 10,800 gallons of water.

Square and Rectangle Pools with variable depths

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

Measuring Length times Width will give you the pool’s surface area. When you multiply this number by the average depth, you’ll have the volume in cubic feet. There are 7.5 gallons in each cubic foot, which is why you multiple the last number by 7.5.

To get the average depth of your pool, add the shallow end depth and deep end depth, then divide by 2. For example, if the shallow end is 4 ft and deep end is 12 feet deep: 4+12 = 16. 16/2 = 8 (Average Depth).

Example: Your in ground pool is 12 Ft wide and 30 Ft long, with a shallow depth of 4 Ft and deep depth of 12 Ft. First, average the depth (example above) to get 8 Ft. Let’s plug the numbers in our formula: 12 x 30 x 8 x 7.5 = 21,600 gallons of water.

Round Pool Volume Calculator

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

What does this mean? Let’s explain: 3.14 is referred to as pi, a mathematical constant. Radius is ½ of the round pool diameter and divided by 2. This will get the radius number. Then, multiple that number (radius) by itself (squared). For example, If you have 20 Ft round pool, divide by 2 and you will have 10 ft (20/2 = 10). Now, multiple that number by itself (10 x 10 = 100). This will be your Radius Squared number in the equation.

Example: Let’s say the average depth of your pool is 8 Ft. and the Radius Squared number is 100. Here is what the formula would look like: 3.14 x 100 x 8 x 7.5 = 18,840 Gallons of Water (Total Volume).

Irregular Pool Volume Calculator

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

The easiest way to calculate the pool volume, is by imagining your pool as two smaller shapes. We will measure these smaller shapes separately and then add them together to discover the total pool volume. You will get each smaller section’s volume by using one of the above formulas.

First, let’s add the total measurement of shape ‘A’ plus shape ‘B’. Then, multiple this number by 0.45. Next, multiple that number by the length of your pool to get the total surface area. Now, just multiple the surface area number by your average depth, followed by 7.5 to get your pool’s total volume in gallons.

Example: Let’s say you have a kidney shaped swimming pool. The first section has a circumference of 20 Ft and the smaller section is 10 Ft. The average depth is 8 Ft and length is 40 Ft. This is what the formula would look like: 0.45 x (20+10) x 40 x 8 x 7.5 = 32,400 gallons of water.

To make things easy, we also created a convenient Pool Volume Chart that shows the estimated amount of gallons for popular pool sizes. Quickly find your size and shape, then use this info to add the recommended amount of pool chemicals to your pool.

Pool Volume Chart

Above Ground

48″ Wall Height

Pool SizeGallons
15′ Round5,300
18′ Round7,600
20′ Round9,400
24′ Round13,600
27′ Round17,200
28′ Round18,500
11×25 Oval6,500
11×30 Oval7,800
15×25 Oval8,900
15×30 Oval10,600
18×33 Oval14,000
18×38 Oval16,100
Above Ground

52″ Wall Height

Pool SizeGallons
15′ Round5,800
18′ Round8,300
20′ Round10,200
24′ Round15,300
27′ Round18,600
28′ Round20,000
11×25 Oval7,000
11×30 Oval8,400
15×25 Oval9,600
15×30 Oval11,500
18×33 Oval15,200
18×38 Oval17,500
In Ground

Average Depth

Pool SizeGallons
12×24 Rect10,800
16×32 Rect19,200
16×36 Rect21,600
18×36 Rect24,300
20×40 Rect30,000
16×32 Oval17,200
18×36 Oval21,700
18×36 Oval21,700
20×40 Oval26,800
17×33 Grec.19,700
17×37 Grec.22,200
20×36 Grec.24,300
20×44 Grec.30,300
16×30 Kid.14,900
16×34 Kid.16,500
20×38 Kid.20,200

There you have it! Now you have the tools to accurately calculate your pool volume in gallons. Knowing this number will help you find the perfect-sized pool equipment to efficiently control your swimming pool. You can also use this important information to follow manufacturer recommendations with pool chemical dosage. For example, Natural Chemistry recommends that you add one capful (4oz) of Pool Perfect + PHOSfree to every 8,000 gallons of pool water. Do you have a 16,000 gallon pool? Add 8oz and you’ll be good to go!

If you have any further questions concerning your pool volume, submit a comment below!

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Brian Champ
When Brian isn't writing pool-related articles, he enjoys anything that will take him outdoors: hiking, biking and trail running ...to name a few. Brian is excited to share his pool knowledge with helpful how-to guides, product reviews, comparisons, and more!