The circumference of a circle is the distance around the outside of the circle. It could be called the perimeter of the circle. How to find the circumference of a circle: The circumference of a circle can be found by multiplying pi ( π = 3.14 ) by the diameter of the circle. If a circle has a diameter of 4, its circumference is 3.14*4=12.56 If you know the radius, the diameter is twice as large.