First, take the depth of the deep end of your pool (in feet), add it to the depth of the shallow end (again, in feet) -- and divide that number by 2. That’s your “average depth.” Now, take that number and apply it to the formula for your pool’s shape:

• For rectangular pools:
  Length (in feet) x width (in feet) x average depth x 7.5 = total gallons
• For oval pools:
  Long diameter (in feet) x short diameter (in feet) x average depth x 5.9 = total gallons