Geometry Tutorials: How to calculate the circumference of a circle

To calculate the circumference of a circle two elements are necessary. Either the diameter or radius of the circle and Pi. In case you have not come across Pi before, it is the number we use in relation with Circle and sphere calculations, as it describes the relationship between a circle's diameter and its circumference. Here it is in it's (no where near) full glory:

Π = 3.1415926535897932384626433...

I say "no where near", because it would stretch on for quite a while yet. For hand calculations most Teachers will be happy enough if you use 3.14159. If you are working for NASA you might want to use the full number however. You don't want that satellite to crash due to inaccuracy;-)!

Here then is how the circumference can be calculated. When using the circles diameter we can use the following formula:

c = Πd

The above of course translates into circumference equals Pi multiplied by diameter. Which of course means if we use the radius we will need to times it by two. Here finally the formula for calculating the circumference using the circle's radius:

c = 2Πr