A 24foot pool can require at least 8,500 gallons of water. However the exact number of gallons will depend on several factors. A simple formula can help calculate the approximate number of gallons in any swimming pool. Several basic measurements are needed to complete the calculation that can be useful for determining chemical doses and how strong of a filter pump motor is needed.
It Really Depends

Several factors must be considered when attempting to determine how much water will fill that 24foot pool. Average depth, shape and measurements are all factors to examine when accurately calculating the pool water capacity. The slightest change in measurements can mean a considerable difference in capacities.
Why You Must Know

All chemicals added to your pool are calculated based on water gallons of your pool. Most chemicals add doses to pools per every 5,000 to 7,000 gallons. Therefore you need to know how much chemicals to add to your pool every time you need to perform basic maintenance. Too little or even too many chemicals can have a negative affect on the swimming water.
Formula

According to Backyard City Pools, which has listed a formula to calculate the pool gallon capacity, there are four things a pool owner must know. To perform the calculation, you must know the pool length, width, average depth and use a special multiplier depending on the size of the pool. The formula (in feet) is, length x width x average depth x multiplier = Gallons. Round and oval pools use the multiplier of 5.9, and rectangular, square or freeform pools use the multiplier of 7.5. Therefore, for a 24foot round above ground pool with an even depth of 4feet, you must calculate, 24 x 24 x 4 x 5.9 to calculate the approximate water capacity of 13,600. An ovalshaped above ground pool such as a 12 x 24foot, at 5feet deep is calculated in the same way. Figure the water capacity by multiplying 12 x 24 x 5 x 5.9 to get approximately 8,500 gallons.
Inground Pools With Sloped Depths

This can be a little trickier than calculating a standard above ground pool. However the formula remains mostly the same. But in addition to the above ground pools, you must figure out the average depth for a pool if it has a sloping depth. Write down the shallowest depth and the maximum depth in feet. For instance the shallow end of your pool is 2 feet and the deepest end is 10 feet. Add 2 + 10 = 12 feet and then divide 12/2 to get an average depth of 6 feet. Now use the formula of length x width x average depth x multiplier = Gallons. If the pool is irregularly shaped, rectangular or square, remember that the multiplier must be 7.5.