Understanding how many gallons are within a square foot of water is useful in determining the amount of water required to fill a structure such as a pool or a pond. Performing this calculation requires you to also know the depth of the area in which the water is located, as you need to have cubic feet to convert to gallons. If you have the depth, you can calculate the gallons of water per cubic foot by performing some simple mathematical operations.

Measure the depth of the structure in which the water is located. Use a tape measure to do this.

Multiply the depth in feet times the width and length of the pool (square footage) to find the cubic feet. For instance, if the pool is 3 feet deep, 10 feet wide and 20 feet long, you would multiply 3 times the product of 10 times 20 to get 600 cubic feet.

Multiply the cubic feet by the amount of water per cubic foot, which is 7.48 gallons. In this example, you would multiply 7.48 times 600 to get 4,488 gallons of water.