Let's say you need to find the area of a circle with a radius of 3 feet. Well, first you need to find the circumference of a circle by doubling the radius. This would give a diameter of 9 feet. You then multiply the 9 ft. by pi, which comes out to about 28 feet^2. That's the approximate area of that circle with a radius of 3 feet.

Let's try one more circle. We're going to do this a little differently. Let's say that the radius is 10 feet. Remember, you first find the circumference. So 10^2 = 100. Then what do you do? You multiply 100 ft. by pi to get the circumference. You can pull your calculator out and do this, or if you know the first few decimals of pi, you know that the circumference comes out as 314.159265... but let's just round to 314 to make this a little easier. So know what? You already know what the diameter is, 100 ft., so know you just multiply 314 ft. by 100 ft. which equals 31,400 ft.^2. That's how you get the area of a circle.

Let's try one more circle. We're going to do this a little differently. Let's say that the radius is 10 feet. Remember, you first find the circumference. So 10^2 = 100. Then what do you do? You multiply 100 ft. by pi to get the circumference. You can pull your calculator out and do this, or if you know the first few decimals of pi, you know that the circumference comes out as 314.159265... but let's just round to 314 to make this a little easier. So know what? You already know what the diameter is, 100 ft., so know you just multiply 314 ft. by 100 ft. which equals 31,400 ft.^2. That's how you get the area of a circle.