The formula C = 2\pi r is used to calculate the circumference C of a circle. In this equation, r represents the radius, which is the distance from the center of the circle to its edge. The symbol \pi (pi) is a mathematical constant approximately equal to 3.14, and it relates the circumference of any circle to its diameter. To find the circumference, you simply multiply the radius by 2 and then by \pi . This means that if you know the radius of a circle, you can easily determine how far it is around the circle's edge using this formula.