Parts of a CircleQuadrants.jpg

circumference is the distance around a circle.

radius is the distance from the centre to any point on the circumference.

diameter is a chord that passes through the centre.
The length of the diameter is twice the length of the radius.




π, the Greek letter pi, is a special number often used in calculations involving circles.

The diameter of a circle, if wrapped around the outside of the circle, would fit just over three times.
(π times)

The value of π is approximately 3.14 (to 2 d.p.).
The fraction with the closest value to pi is 227 or 317



Perimeter of a Circle


The perimeter of a circle is called the circumference

The length of the circumference (C)

C = 2πr

= πd


Area of a Circle

The area of a circle is given by the formula

A = πr2