How to Calculate Pool Volume (Gallons)

    Why Is It Important to Know Your Pool's Volume?

    There are some good reasons why you should know your pool volume. 

    It helps in order to add the right amount of chemicals when balancing and sanitizing because too much can be harmful to your pool and equipment and be uncomfortable for swimmers. Not adding enough chemicals for your pool size can lead to increased germs and algae growth, which can be costly to fix.

    Many chemical labels provide a dosage rate of 5,000 or 10,000 gallons, so you'll want to scale up or down from there as needed when adding chemicals. 

    You need to know how much water is required to fill the pool initially and make up for any losses over time. The volume in gallons will determine the water pool needs

    Other reasons for knowing the volume of your pool have to do with properly sizing new pool equipment and determining how long your pump should run.

    If it runs too long, you're wasting electricity, and if it runs too little, you won't be circulating the proper amount of water through the filter. You should be circulating about your entire pool volume once per day or more in warmer areas, or if you're addressing water treatment issues.


    How Many Gallons is My Pool?

    To calculate the number of gallons in your pool, you will need to know the dimensions of your pool. Once you have that information, you can use a formula to calculate the volume of the pool in cubic feet, and then convert that to gallons.


    Formula for Volume


    Length x Width x Height

    Rectangular Prism

    Length x Width x Height

    Triangular Prism

    0.5 x Base x Height x Length


    π x Radius^2 x Height


    (1/3) x π x Radius^2 x Height


    (4/3) x π x Radius^3


    (1/3) x Base Area x Height


    When it comes to figuring out the volume of your pool, you might be lucky enough to still have the paperwork from your pool builder or manufacturer which often lists the gallon capacity. If not, we're going to show you how to calculate it with some simple measurements and a little math.

    You'll need a tape measure, pencil, and paper, and of course, a calculator always helps to start off. 

    Once you have calculated the volume of your pool in cubic feet, you can convert it to gallons by multiplying by 7.5.

    Gallons = Length x Width x Average Depth x 7.5

    The factor of 7.5 is used to convert the volume of the pool from cubic feet to gallons.

    For example, if you have a rectangular pool that is 20 feet long, 10 feet wide, and has an average depth of 5 feet, the volume would be:

    • Volume = 20 x 10 x 5 = 1000 cubic feet

    To convert to gallons, you would multiply by 7.48, so:

    • 1000 x 7.5 = 7,500 gallons

    Therefore, your pool is 7,500  gallons.

    Calculate Pool Volume

    Different Volume Calculations for Pool Shapes

    For rectangular or square pools, you multiply the length by width by average depth by 7.5 to get your approximate volume. So, for example, if your pool is 28 feet long, 14 feet wide, and has an average depth of five and a half feet, you'll multiply 28 * 14 * 5.5 * 7.5, which gives you an approximate pool volume of 16,000 gallons. 

    Rectangular, Freeform

    For circular pools and hot tubs, the diameter is your widest point with 1/2 that measurement being the radius. You can figure out the average depth of your pool by measuring the depths at the shallowest and deepest ends, then adding them together and dividing by two. If your pool happens to be the same depth throughout, then you made out easy for this part. 

    Francisco Pardo

    For circular pools and hot tubs, you multiply π, which is 3.14 times the radius, times the radius, and again times your average depth by 7.5.

    If your pool's oval, you'll multiply π, which again is 3.14 times the length by the width of your pool, times .25 times your average depth. Then you multiply that by 7.5 and that'll give you your approximate volume and gallons. 

    Oval Shaped Inground Pools - Latham Pool

    If you have a kidney-shaped pool, you'll want to get the measurements of your two widest points. Mark one with A and the other with B. You'll add A and B together and then multiply that number by the actual length of your pool. Once you have that, multiply it by .45, then multiply it by your average depth and lastly by 7.5 and that'll be your volume for a kidney shape pool. 

    Kidney Shape Pools

    For in a regular shape or free-form pool, you'll want to take the longest length of your pool times the widest width and multiply that number by your average depth. Then take that and multiply it by 5.9 to calculate your approximate volume in gallons. 

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