Circles for Kids: Circumference and Area with Pi (Grade 7 Math)

Hi, I'm Luna from DoodleBeez. Today we are measuring circles. The center is the middle point. The radius goes from the center to the edge. The diameter goes all the way across, so it is two times the radius.

Every circle has a special number called pi. If you divide any circle's circumference by its diameter, you always get pi. Pi is about three point one four, and its digits go on forever.

Circumference is the distance around a circle. Circumference equals pi times the diameter. Since the diameter is two radii, it also equals two times pi times the radius.

A wheel has a diameter of ten centimeters. Multiply three point one four by ten. The circumference of the wheel is about thirty one point four centimeters.

Area is the space inside. Area equals pi times the radius squared. If the radius is three centimeters, square it to get nine. Three point one four times nine is about twenty eight point two six square centimeters.

Be careful! Area uses the radius, not the diameter. If you are given a diameter of eight, halve it first. The radius is four, four squared is sixteen, and sixteen times three point one four is about fifty point two four.

Now it's your turn. A circle has a radius of five centimeters. Find its circumference and its area. Pause and try. The circumference is about thirty one point four centimeters. The area is about seventy eight point five square centimeters.

Great job! Remember, pi is about three point one four. Circumference is pi times the diameter, and area is pi times the radius squared. Practice circles in Middle School Math at doodlebeez.com. See you next time!