Area of a Circle

Contributor: Ashley Nail. Lesson ID: 13410

Hurricanes are huge storms that cover a lot of area. Have you ever wondered how to find the area of these super storms? Learn how to find the area of circles using pi and a formula.

categories

Geometry, Middle School

subject
Math
learning style
Visual
personality style
Lion, Beaver
Grade Level
Middle School (6-8)
Lesson Type
Quick Query

Lesson Plan - Get It!

Audio:

A hurricane is off the coast of Florida. Satellite images show that the storm is 296 miles wide. Meteorologists want to find out how much area the hurricane will cover when it reaches land.

This is important information because it will help cities warn its citizens to prepare for the storm.

We can use geometry to help!

  • How do you think meteorologists will use geometry to estimate the area of a hurricane?
  • A hurricane most resembles what shape?

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

hurricane circle

In order to find how much land this storm will cover, we need to find the area of this circle!

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

circle area

Much like circumference, we 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.

circle measurements

The diameter is also 2 times the radius, which also means the radius is half the diameter.

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

Look at the information we have about the hurricane:

The storm is 296 miles across.

We know the diameter of the circle!

hurricane diameter

To find the area, we 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

hurricane radius

Now we can use the formula to find the area of the circle!

For pi, use the number 3.14:

area equation

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.

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