Circles

A circle is a flat, round shape. Every point on the edge of a circle is the same distance from the middle. That middle point is called the center. Circles do not have any corners or straight sides. You can see circles in wheels, clocks, and coins.

Parts of a Circle

A circle has special parts with names. The radius is the distance from the center to the edge. The diameter is the distance all the way across the circle through the center. The diameter is always twice as long as the radius. The distance around the outside of a circle is called the circumference.

The Number Pi

There is a special number called pi that helps us work with circles. Pi is about 3.14. If you divide the distance around a circle by its diameter, you always get pi. This is true for every circle, big or small. Pi is used by builders, engineers, and scientists.

Fun Facts

• Pi Day is celebrated on March 14th because the date looks like 3.14.
• The wheel was one of the most important inventions in history.
• A sphere is like a 3D circle, like a ball or a globe.

Did You Know?

Pi is a decimal number that goes on forever without ever repeating.