Area of a Circle

Lesson Plan - Get It!

Audio:

• A hurricane most resembles what shape?

Definitely not a square or triangle. A hurricane is similar to a circle!

To find how much land this storm will cover, you need to find the area of this circle!

Remember that area is the space that covers the inside of a shape.

Much like circumference, you use a formula to find the area of a circle. (To review using a formula to find the circumference of a circle, visit our lesson found under Additional Resources in the right-hand sidebar.)

The area of a circle is pi multiplied by the radius squared:

Area = ∏ r²

Circles have two main measurements: radius and diameter.

The diameter is a straight line that goes straight across a circle, passing through the center. The radius starts at the center of a circle and measures the distance to the outside boundary.

The diameter is also 2 times the radius, meaning the radius is half the diameter.

When finding the area of a circle, you use the radius measurement in your formula. However, that does not mean the diameter is useless information!

Look at the information you have about the hurricane:

The storm is 296 miles across.

You know the diameter of the circle!

To find the area, you need to know the radius to plug into the formula.

The radius is half of the diameter. So, to find the radius of this circle, all you have to do is divide the diameter by 2:

D ÷ 2 = r

296 ÷ 2 = 148

r = 148

Now, you can use the formula to find the area of the circle!

For pi, use the number 3.14:

Now the meteorologists know the area the hurricane will cover once it hits land! The hurricane will cover about 68,779 square miles! That is a lot of people to warn about the storm!

• Are you ready to find the area of more hurricanes?

Move on to the Got It? section to practice finding the area of circles and helping meteorologists measure hurricanes.