The circumference of a circle is the distance around its outer edge. It is a fundamental concept in geometry and is often used to calculate the size and dimensions of circles. The formula for finding the circumference of a circle is C = 2?r, where r is the radius of the circle. This means that the circumference is equal to twice the radius times pi (?), which is a mathematical constant approximately equal to 3.14159.

Circumferences are used in many real-world applications, such as calculating the length of a wire needed to make a circular fence, the distance traveled by a wheel in one revolution, or the amount of material needed to wrap around a cylindrical object. Understanding how to calculate circumferences is important in fields like engineering, architecture, and physics.

Circumferences also have a relationship with the diameter of a circle, which is the distance across the circle through its center. The diameter of a circle is equal to twice the radius, so the circumference of a circle can also be calculated using the formula C = ?d, where d is the diameter. This relationship between circumference, radius, and diameter is essential for solving various geometry problems involving circles.