By
eHow Home & Garden Editor
Difficulty: Moderately Easy
Step1
Calculate the circumference or width and length of the pool, and then measure the depth of the pool. To calculate volume you needed height, width and depth.
Step2
Use the appropriate multiplier. Rectangular, square and free-form swimming pools use a multiplier of 7.5. Round and oval pools have a multiplier of 5.9.
Step3
Apply this simple calculation: Length x Width x Average Depth x Multiplier = Gallons. For example, if your pool is 20-feet long, 10-feet wide and has an average depth of 6 feet, you'll need 1200 gallons of water (20 x 10 x 6).
Step4
If your pool is round, multiply Circumference x Average Depth X Multiplier. So a pool with a circumference of 60 feet with an average depth of 5 feet can contain 1770 gallons of water (60 x 5 x 5.9).