Measuring Circles

Contributor: Meghan Vestal. Lesson ID: 11405

Have you ever tried to bend a ruler around a circle to measure its circumference? There is an easier way, and you will learn that method, 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!


How would you measure the circumference of this circle? What tool(s) would you use?

Welcome back to the series, Measuring Circles.

Before you begin learning to measure circles, let's take a few minutes to review what you learned in the previous Related Lesson, found in the right-hand side.

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

When you are finished labeling each of the parts, show your work to a teacher or parent. If you cannot remember these four parts, go back to the previous lesson and find the answer.

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? Tell your teacher or parent.

To find the diameter, radius, and chord, use a ruler to measure each of the parts. 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? Tell your teacher or parent.

To measure circumference, you need a ruler and piece of yarn. Lay the yarn over top of the outline of the circle, creating a circle with the yarn. You want to create a yarn circle that is exactly 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 length of the circumference. Then, pick the yarn up and straighten it out into a straight line. Now, it is easy to use your ruler to measure the circumference!

Since you have been given instructions on how to find the circumference, diameter, radius, and chord, move on to the Got It? section to practice measuring circles and see the relationships among the parts of a circle.

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