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How to Calculate the Number of Gallons in Your Pool


Knowing the volume of your swimming pool is tremendously important. By knowing how much water is needed to fill or refill your pool each season, you are able to anticipate your water bill costs more accurately. Many pool chemicals and pieces of pool equipment are only effective in swimming pools up to a certain number of gallons. Incorrect dosage of pool chemicals (either too much or not enough) can be easy without knowing the number of gallons in your pool, which could lead to chemical imbalance.

With some simple math, approximating the “gallonage” of your swimming pool can be a quick and easy process. Below is a list of formulas to help determine your pool’s volume. Each formula below depends on which shape pool you have.

Be sure to use feet as the unit of measurement for all of your pool dimensions! Many above ground pools measure wall height in inches rather than feet, so you will need to convert this measurement to get your depth in feet (simply take your inch measurement and divide by 12).

You will need to know the Average Depth of your pool for each formula. For flat bottom pools, the average depth is simply the depth. For pools that have variable depths (a shallow end and a deep end), you will need to calculate the Average Depth by adding together the depth of the shallow end of your pool plus the depth of the deep end of your pool and then dividing that number by 2.



Rectangular & Square Pools 



Length × Width × Average Depth × 7.5

Example: 16’ × 32’ rectangular pool with 3’ shallow end and 7.5’ deep end



Average Depth: 3 + 7.5 = 10.5, 10.5 ÷ 2 = 5.25



16 × 32 × 5.25 × 7.5 = 20160 Gallons







Round Pools



Diameter × Diameter × Average Depth × 5.9

Example: 24’ round pool with a flat bottom, 48” wall height (converted to 4’)

24 × 24 × 4 × 5.9 = 13593.6 Gallons




Oval Pools



Length × Width × Average Depth × 6.7

Use the longest & widest points of your oval pool, respectively, for the Length and Width measurements.

Example: 12’ × 24’ oval pool with a flat bottom, 52” wall height (converted to 4.33’)

12 × 24 × 4.33 × 6.7 = 8355.17 Gallons




Kidney Pools



Average Width × Full Length × Average Depth × 7.0

Average Width is determined by adding the widest points of your pool at each end and then dividing by 2.

Example: 32’ long kidney pool, with 14’ and 17’ widths, with 3’ shallow end and 6’ deep end

Average Width: 14 + 17 = 31, 31 ÷ 2 = 15.5

Average Depth: 3 + 6 = 9, 9 ÷ 2 = 4.5

32 × 15.5 × 4.5 × 7 = 15624 Gallons


It’s important to remember that these figures are close approximations and may vary slightly from the true number of gallons in your pool. However, these calculations will go a long way into making sure you are maintaining your pool properly.


Greg The Pool Guy General Maintenance