Circumference of Circle
The circumference of a circle is a length of an around arc. How to imagine the circumference of a circle? For example, you have a tire and make a point on its edge. After one round move, the point goes a distance which equals to the circumference of a circle.
To calculate the circumference of a circle we need to know its diameter or its radius and the pi number (Ludolph's number). The pi number is a constant and equals to 3.141592... In a circle, the diameter is d = 2 × radius "r". The elementary unit is one metre (1 m).
d=2 × r, also r = d / 2
Circumference of Circle - formula
Circumference of Circle = Ludolph's number × diameter
Circumference of Circle = 2 × Ludolph's number × radius
C = π × d = 2 × π × r