Calculating the circumference A circle is one with an equal center and an equal radius. Circles have different properties, such as area, perimeter, and radius. The circumference of a circle is calculated as the product of the π of pi and the number equal to the radius. The perimeter formula is C = 2 * pi * r. This is derived from the fact that the circumference of a circle with a radius of 1 is 2π. Circles play a particularly important role in shapes and are used in a wide range of fields. It is used in various fields such as physics, astronomy, and design.