To figure out how many gallons of water a pool holds, calculate the surface area and multiply by the depth of the pool to obtain a figure for the cubic volume. Multiply the cubic volume by 7.5 for a square or rectangular pool, 7 for a kidney-shaped pool, or 5.9 for a round or oval-shaped pool.
The surface area of a square or rectangular pool is the length times the width. If the pool is L-shaped, divide it into two rectangles, calculate the surface area of each rectangle, and add them together. For other irregular shapes, try to picture them as combinations of regular shapes, and add the measurements of each separate shape.
To find the surface area of a round pool, square the diameter. For an oval pool, multiply the longest length by the longest width. In figuring the surface area of a kidney-shaped pool, take measurements of the shorter and longer widths, divide the total by two, and multiply that by the length. Though these calculations result in inaccurate total surface areas and cubic volumes for round, oval- and kidney-shaped pools, the smaller final multipliers of 7 and 5.9 make up the difference.
To figure the depth, if the pool is the same depth throughout, simply measure the distance from the bottom of the pool to the top of the water. If it has a gradual slope, measure the shallow end and the deep end, and divide by two. If the bottom is irregular, take measurements in several places, and divide by the number of measurements you take.