Question: how to calculate how much water is needed to fill a pool?
Answer: Length x width x depth x 7.5 = volume (in gallons) Length times width gives the surface area of the pool. Multiplying that by the depth gives the volume in cubic feet. Since there are 7.5 gallons in each cubic foot, multiply the cubic feet of the pool by 7.5 to arrive at the volume of the pool, expressed in gallons.