The amount of water in a swimming pool determines the amount of chemicals needed to maintain the water in the pool. There are a number of different pool sizes and shapes, which can make it difficult to calculate the water in swimming pools. There are formulas and methods to make it simple to calculate pool water volume so you can add the proper amount of chemicals based on the amount of water being treated.
Measure the width, length and average depth of the pool.
Determine the average depth of a sloped or graded pool by measuring the depth of the shallow end, the depth of the deep end, adding the two together and divide the sum by two. For example, a pool with a shallow end of 3 feet and a deep end of 9 feet, is 12 feet divided by 2, which is an average depth of 6 feet.
Calculate the number of gallons of water in a square or rectangle pool by multiplying the length, width and average depth and multiplying the product by 7.5. For example, for a pool that is 32 feet long, 16 feet wide, with an average depth of 6 feet, the calculation is: 32 x 16 x 6 x 7.5 = 23,040 gallons of water.
Calculate water in a round swimming pool by multiplying the pool width by itself, multiply by the depth and then multiply by 5.9. For example, for a round pool that is 12 feet across and 4 feet deep, multiply 12 x 12 x 4 x 5.9 = 3,398 gallons of water.
Calculate water in oval swimming pools by multiplying the pool width by the length, multiply by the depth and then multiply by 5.9. For example, for a round pool that is 12 feet across, 18 feet long and 4 feet deep, multiply 12 x 18 x 4 x 5.9 = 5,098 gallons of water.
Calculate the water lost during evaporation or gained during rain when measuring chemicals. A couple of inches of water has a large impact on the amount of water in a pool.