Pool Volume Calculator: How Many Gallons Are in My Pool?

If you have a pool at home, you may wonder, “How many gallons of water are in my pool?” It's helpful information to know as it will help you calculate how many chemicals you need for pool maintenance, as well as what size pool heater you'll need. 

It’ll also help you estimate the cost of filling your pool with water. Fortunately, there are relatively simple formulas you can use to calculate pool gallons based on factors like the size and shape of your pool.

Pool Volume Basics

To calculate pool volume, you'll need to know several metrics depending on the shape of your pool.

• Length and width: If you have a rectangular pool, you'll need to measure its length and width.

• Surface area: You also need to know a rectangular pool's surface area, which you can find by multiplying its length by width.

• Diameter: For circular pools, you'll need to know the diameter, which is how long the pool is from one side to the other.

• Radius: You’ll also need the radius for circular pools, which is calculated by dividing your pool's diameter in half. 

• Depth: Regardless of your pool shape, you'll need to measure how deep it is to calculate pool volume. 

• Pi: For circular pools, you’ll need to multiply by 3.14.

You should also consider the slope of the bottom of your pool. If your pool slopes down and gets deeper in certain areas, that will affect your volume calculations.

Rectangular Pool Volume

Use this formula: Length x width x depth x 7.5 = volume in gallons

To calculate the volume of a rectangular pool, you'll first need to measure the length and width of your pool in feet. Next, measure how deep your pool is in feet. If your pool is one consistent depth, i.e., it doesn't have a slope, then all you need to do is multiply its length, width, and depth by 7.5 to determine how many gallons it holds.

If your pool has multiple depths, such as a shallow end and a deep end, you'll need to find the average depth across the pool before doing the above calculation. To find the average, measure the depth at the deepest and shallowest points. Then, add them together and divide the resulting number by two.

Use this formula: (Deepest depth + shallowest depth) / 2 = average depth

Once you have the average depth, you can perform the following calculation to find your pool volume:

Length x width x average depth x 7.5 = volume in gallons

Round or Circular Pool Volume

Use this formula: 3.14 x (radius x radius) x depth x 7.5 = volume in gallons

When calculating circular pool volume, you'll be working with its diameter and radius, rather than its length and width. You'll also be using your pool's depth and the value of Pi, which you can round to an even 3.14 for these formulas. 

To find a circular pool's diameter, measure it from one side to the other from the longest points. Once you find the diameter, divide it by two to find the radius.

Diameter / 2 = radius

In addition to the radius, you'll need to measure your pool's depth in feet. If your pool has multiple depths, then you'll find the average using the average depth formula:

(Deepest depth + shallowest depth) / 2 = average depth

Now that you have all of your metrics, just plug them into the following formula. Note that you'll use the radius twice.  

Oval Pool Volume

Use this formula: (Length x width x 3.14 / 4) x average depth x 7.5 = volume in gallons

Oval pool volume calculations are similar to circular pools but with one extra step. To calculate oval pool volume, you'll first find the length and width of the pool, measuring them at their longest points. You'll then multiply the length and width by 3.14 and divide the resulting number by 4 to find the surface area. Finally, multiply that number by the average depth and 7.5 to determine the volume. 

Use this formula: (Length x width x 3.14 / 4) x average depth x 7.5 = volume in gallons

Irregular or Freeform Pool Volume

Finding the volume of irregular and freeform pool shapes is a little trickier than other shapes since it requires additional steps. But the good news is you won't need to use any other calculations besides the ones already listed in this article. 

For these pool shapes, you'll want to break the shape down into smaller, more standard shapes. For instance, if you have a kidney-shaped pool, you can find the approximate volume by breaking it up into two circles and using the circular pool calculations outlined above.

When in Doubt, Hire a Pro to Measure Your Pool

If your pool shape is highly irregular, or you simply don't want to fuss with the math, you can always call a local pool pro to help. A pool professional can determine how many gallons your pool holds, as well as give advice about heater size, appropriate chemicals, and pool care mistakes to avoid.