Another Round of Pi

Some of you may have discussed pi with students on March 14, often called Pi Day. Are you ready for another look at that special number that is very close to 3.14?

Many students are confused by the formulas for circumference and area of a circle. In CCSS, circle relationships and formulas are to be taught in Grade 7, standard 7.G.4. To help my students with circumference and area, I've developed a visual approach.

First consider the circumference or distance around a circle. I ask leading questions to help students estimate the circumference as a multiple of the length of the diameter, based on these diagrams.

For area, I help students relate the area of a circle to the square of the radius.


I help students see that when the diameter of a circle is 1, the circumference is pi! And, if the radius is 1, the area is pi! If students visualize the relationships between parts of circle, they are more likely to develop an understanding of the formulas.