You will need

- Paper, pen, calculator

Instruction

1

First we find the diameter D (diameter is a straight line which connects the two most remote from each other point of the circle always passes through the center). This will double the radius of the circle r: D=2r.

2

Now you have all the data in order to find the length of circumference L. Use the formula L=?D. Number ? is the ratio of a circle's circumference to its diameter, it is the same for all circles and is approximately equal to 3.14. Thus, to calculate circumference, multiply 3.14 by the diameter..

3

Knowing the radius, you can also calculate the area of a circle by multiplying the number ? (3.14) times the radius squared: S = ?R2.

Useful advice

The number π (read as PI) is an infinite non-periodic decimal fraction: 3,141592653589793238462643... For computational convenience it is usually shortened to 3.14.