Arithmetic Grade Six

Lesson One Hundred Seventy-two: Circumference and Area


The circumference of a circle is the distance around a circle. It's kind of like perimeter except for a circle. Here's the formula to find the circumference of a circle providing that you know the radius: 


	  circumference = PI * 2 * radius
As you know the radius is half of the diameter and so this formula could also be expressed as circumference = PI * diameter.

The value we use for PI (symbol: π) in this lesson is 3.14. Another commonly used approximation of PI is 22/7. PI is a never ending decimal value which starts something like this 3.14159, but which actually goes on forever.

Here's a sample problem: 


  Find the circumference of the following circle:

      

  Circumference = PI * 2 * 6 = 3.14 * 12 = 37.68 units
Here's another example: 

  Find the circumference of the following circle:

      

  C = PI * 2 * 3 = 3.14 * 6 = 18.84 units

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