Circumference, Radius, Diameter, Oh My!

Even though middle school geometry can be tough, there's no reason to fear the friendly circle. Big words like "circumference," "radius," and "diameter" may sound intimidating, but they're just fancy words for different measurements of a circle. Here's a quick, kid-friendly intro to those geometry terms, and a fail-safe way to calculate circumference, no matter what!

Circumference

Circumference is defined as the distance around a closed curve (i.e. a circle or ellipse). To illustrate the concept of circumference, sit at the table with your child and take a string (a shoelace or piece of  yarn works great). First, have her measure the string with a tape measure or ruler. Write down the measurement; let’s say it’s 18 inches. Now, tell her to make a circle on the table with the string, with one end touching the other. Explain to her that the circumference of the circle is the length of the string: the distance all the way around the circle. Ask her what the circumference of that circle is. If she can figure out that it’s 18 inches, she gets the basic concept.

Diameter

The next thing to illustrate is the idea of diameter. The diameter of a circle is the length of a straight line which passes through the center of the circle and ends at the circle's edge. To illustrate this concept, take another string and ask your child to stretch it right across the middle of the circle. Cut off the excess that is hanging over the sides of the circle, if possible. Explain that the distance of that string from one edge of the circle to the other is the diameter. The diameter is the distance across the middle of a circle.