Determining the square feet of a circular pool is the same as determining the area of a circle. Calculate the area of a pool so you'll know how much land a round pool will take up on your property. The formula for calculating the area of a circle is pi times radius squared.
Measure from one side of the pool through its center to the opposite side with the tape measure. This number is the pool's diameter. For example, say a pool has a diameter of 10 feet.
Divide the diameter in half to determine the radius. In the example, 10 feet divided by two equals a radius of 5 feet.
Multiply the radius by itself. In the example, 5 feet times 5 feet equals 25 feet squared.
Multiply the number calculated in Step 3 by pi to determine the area of the pool. Pi is generally estimated as 3.14. In the example, 25 feet squared times 3.14 equals an area of 78.5 square feet.