The circumference of a circle is the distance around the circle. It can be calculated using the formula C = 2\pi r , where C represents the circumference, r is the radius, and \pi (approximately 3.14) is a constant that represents the ratio of the circumference to the diameter of any circle. The diameter of a circle is twice the radius, so another formula for circumference is C = \pi d , where d is the diameter. Understanding the circumference is important in various fields, including geometry, engineering, and everyday activities like measuring circular objects.