The average round pool is 21 feet in diameter and 48 inches deep. It can hold 13,500 gallons of water. Robelle says that a round pool that is 21 feet across and 52 inches deep can hold 14,500 gallons.
To figure out how much water a round or oval pool can hold, multiply the average depth by the length times the width times 5.9. For a square or rectangular pool, you multiply the average depth by the length times the width times 7.5.
By accurately calculating water capacity, pool owners can figure out how much and what kind of chemicals they need to clean the pool and keep the pH balance of the water.