## LESSON: Circumference of Circles

### READ: Find the Circumference of a Circle Given the Diameter or Radius

**Find the Circumference of a Circle Given the Diameter or Radius**

Now that you know about the relationship between the diameter of a circle and the circumference of the circle, we can work on figuring out the circumference using a formula and pi.

**To figure out the circumference of the circle, we multiply the diameter of the circle times pi or 3.14.**

**Remember, whenever you see the symbol for pi, you substitute 3.14 in when multiplying.**

Example 1

*Find the circumference.*

**The diameter of the circle is 6 inches. We can substitute this given information into our formula and solve for the circumference of the circle.**

**Our answer is 18.84 inches.**

**What about if we have been given the radius and not the diameter?**

Example 2

*Find the circumference.*

**Remember that the radius is one-half of the diameter. You can solve this problem in two ways.**

**Double the radius right away and then use the formula for diameter to find the circumference.****Use this formula when you have been given the radius of the circle.**

Let’s use the formula to find the circumference of the circle.

**Our answer is 25.12 cm.**