# The Basics of Circumference

Circumference is like perimeter except it’s only used for circles. Here are some basic rules you need to know before even starting circumference:

Center Point – The center of the circle

Radius – From the Center Point, it will only reach either the left or right side

Diameter – The radius x2, meaning that it reach both the left and right side

Circumference – Perimeter of a circle

Quadrant – A quarter (1/4, 0.25, 25%) of the entire circle

Pi () – It is used in circumferences, trigonometry, etc. It is used in formulas and it will be either the number 3.14 or 22/7. For the circumference formula, it is 2r (meaning 2x 3.14 or 22/7 x radius. Now on to the real thing.

We can be doing questions like “Billy likes to go cycling, his bike has wheels of diameter 75, he has invented a counter for his bike which counts the number of revolutions the wheels make, one day the counter shows 380 revolutions, how far had billy cycled?”

But since we are just starting… we should just start off with easy (simple) questions.

First, let’s try to find the circumference of a circle : Radius : 7cm – Diameter : Unknown – Circumference : Unknown

First, we need to know the formula… the formula for circumference is 2 (pi) r meaning 2 x 22/7 x 7. We can strike out both the sevens since they are both divisible and we are directly left with 2 x 22. 2 x 22 is 44 so the circumference of the circle is 44cm. In order to find the diameter, all we’ve got to do is multiply the radius by 2, which in this case.. the diameter is 14.