Measuring Circles

Contributor: Meghan Vestal. Lesson ID: 11405

Have you ever tried to bend a ruler around a circle to measure its circumference? Learn an easier way and get a slice of pi as you relate the parts of a circle!


Geometry, Measurement and Data

learning style
personality style
Grade Level
Middle School (6-8)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

Audio: Image - Button Play
Image - Lession Started Image - Button Start
  • How would you measure the circumference of a circle? 
  • What tool(s) would you use?

In the previous Related Lesson, found on the right-hand side, you learned the four parts of a circle.

Draw a circle on a piece of paper. Then, draw and label the following parts. Make sure to use a ruler or straightedge to help you create straight lines.

  • circumference
  • diameter
  • radius
  • chord

In this lesson, you will learn how to measure circumference, diameter, radius, and chord.

Finding the diameter, radius, and chord is easy.

  • How do you think you should measure each of these parts?

To find the diameter, radius, and chord, use a ruler to measure each part. Throughout this lesson, you will measure everything in centimeters.

Finding the circumference is a little more challenging. In most cases, you cannot straighten the circumference out, so you have a nice straight line to measure.

  • How do you think you should measure to find the circumference?

To measure the circumference, you need a ruler and a piece of yarn. Lay the yarn over the top of the circle's outline, creating a circle with the yarn. You want to create a yarn circle the same size as the circle you are trying to measure.

Once you have created the yarn circle, cut the yarn so it is the exact circumference length. Then, pick the yarn up and straighten it into a straight line.

Now, it is easy to use your ruler to measure the circumference!

Now that you know how to find the circumference, diameter, radius, and chord, move to the Got It? section to practice measuring circles and seeing the relationships among the parts of a circle.

Image - Button Next