How to Calculate Pool Capacity Gallons

You can calculate the gallon capacity of your pool by measuring its dimensions and multiplying them by a fixed multiplier. You need to know how the pool's length, width and depth--and if it is a variable depth. To obtain the most accurate calculation, measure the length and width of the inside of your pool. Calculating the pool’s volume will enable you to determine how much chlorine and other additives you need.

Things You'll Need

  • Measuring tape
  • Calculator
  • Ladder
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Instructions

  1. Rectangular or Square Pool

    • 1

      Determine the length and width of your pool by measuring them with a measuring tape. You may need to reposition the tape, so make a mark each time you move the tape. Record each measurement.

    • 2

      Determine the average inside depth of your pool. You may need to use a ladder and to move the tape. If the pool has a deep end and a shallow end, measure both, add the numbers and divide the total in half to obtain the average depth. For example, if the deep end is 10 feet and the shallow end is 6 feet, the total is 16 feet and the average depth is 8 feet. If the average ends in a half-foot, convert it to a decimal. For example, if deep end is 10 feet and the shallow end is 7 feet, the total is 17 feet, and the average is 8.5 feet.

    • 3

      Multiply the three dimensions by each other to obtain the pool’s capacity in cubic feet. For example, if the width is 18 feet, the length is 22 feet and the average depth is 8 feet, multiply 18 by 22 by 8. The result: 3,168 cubic feet.

    • 4

      Multiply the number of cubic feet by 7.47 to determine the number of gallons if your pool is equally deep everywhere. For example, if you have an 18-by-22-by-8-foot pool the volume is 3,168 cubic feet. Multiply by 7.47. The result: 23,665 gallons. If your pool has a deep and shallow ends, multiply the cubic footage by 5.9 instead of 7.47.

    Round Pool

    • 5

      Determine the inside radius of your pool. The radius is one-half of the pool’s diameter--that is, one-half the length from a point on one side to a point directly opposite it. For example, if the diameter is 24 feet, the radius is 12 feet. If the radius ends in a half-foot, convert it to a decimal. For example, a diameter of 23 feet has a radius of 11.5 feet.

    • 6

      Square the radius by multiplying the number by itself. For example, if the radius is 12 feet, multiply it by 12. The result: 144.

    • 7

      Multiply the square of the radius by 3.1417. For example, multiply 144 by 3.1417. The result: 452.405.

    • 8

      Determine the depth by measuring it. If the measurement ends in a half-foot, convert it to a decimal. You may need to stand on a ladder and move the measuring tape.

    • 9

      Convert the measurements to cubic feet by multiplying the result in Step 3 by the depth to obtain the pool’s capacity in cubic feet. For example, multiply 452.405 by a depth of 10 feet. The result: 4,524.

    • 10

      Multiply the number of cubic feet by 7.47 to convert the cubic feet into gallons. For example, multiply 4,524 by 7.47. The result: 33,794. This is the water capacity in gallons of a 24-foot-by-10-foot pool.