Circumference
Circumference is the distance around the outside edge of a circle.
A round cake pan has a rim you can trace with your finger. The path your finger travels all the way around that rim is the circumference. A bigger pan has a longer path around its edge. A smaller pan has a shorter path.
Explaining circumference by grade level
Think about wrapping a string around a round plate. The length of that string is the distance all the way around. Every circle has this same kind of edge you can measure. A bigger circle needs a longer string to go around it.
Projects that explore circumference
The circumference of a circle can be approached step by step using polygons. In this project, you draw regular polygons around a circle of radius 1 and keep doubling the number of sides. Each polygon's perimeter gets closer to the circle's circumference, showing that the distance around a circle is a fixed value that polygons can approximate but never quite match.
Every circle's circumference connects to pi through the fixed ratio C = πd, and ancient mathematicians narrowed in on that value by drawing polygons inscribed in and around circles. The more sides a polygon has, the closer its perimeter gets to the true circumference. You calculate pi by averaging the perimeters of polygons drawn inside and around a circle, and the error ratio follows a clear pattern — shrinking in a predictable way as you add more sides.