Lesson objective: Compute the circumference of a circle when given the radius or the diameter.

This lesson helps to build procedural skill by solving the formula for circumference (C = πd). Circle diagrams are used here because they support the conceptual relationship between circumference and diameter. This work develops students' understanding that the ratio of the measures of circumference and diameter is a constant which we call Pi (π).

Students engage in Mathematical Practice #8 (Look for and express regularity in repeated reasoning) as they use the mathematical formulas for circumference and the circle diagrams to find the circumference of a given circle.

**Key vocabulary:**

- circle
- circumference
- diameter
- pi (π)
- radius

**Special materials needed:**