Lesson Plan Title : Finding circumference, diameter, and radius

Age Range:

Grade 6 through Grade 8 (Middle School)

Overview and Purpose:

This activity will allow students to measure the circumference, diameter, and radius of a circle in a hands-on way. By being able to manipulate a circle and stretch it out the idea of circumference will be more concrete. Students will use each other, desks, and chairs to create circles that can be measured.


The student will be able to measure a circle to find the circumference, diameter, and radius.


Students' desks and chairs

2 different colored balls of string

25 foot tape measure

Math journals

White board and markers


Discuss the definitions of circumference, diameter, and radius. Write them on the board and have students copy them into their math journals. Explain that the students are going to practice measuring circles.

Clear a space in the middle of the room and have several students make a circle. Pass a ball of string around to the students and cut it when it gets back to the first student. Explain that this piece of string represents the circumference.

Line other students across the center of the circle and explain that they represent the diameter. Pass a different ball of string down this line of students.

Ask students where the radius is. Explain that the radius is half of the diameter. Show them that you can accurately find the radius by folding the diameter string in half.

Have the students stretch the circumference string out and measure it and the diameter one. Have them divide the diameter in half to get the radius.

Repeat this exercise several times with different size circles and using different items. If students are using their desks they can wrap the string around the outside of their desks to hold it in the shape of a circle. Students will enjoy coming up with unique ways to make the circles and finding items they can use to represent diameter.


This lesson is a great lead in to teaching the formulas students will need to memorize to measure circumference, diameter, and radius of circles. A smaller version of this lesson can be used as homework or in a math center with short pieces of string, rulers, and teacher created worksheets.