The circumference of a circle is calculated by multiplying pi by the diameter, or 2 pi times the radius. The diameter or radius value is required to calculate circumference.
The circumference is the distance around a circle. The Greek letter pi is an irrational number beginning with 3.14. If the diameter of a circle is 1, then the circumference of a circle is pi, or 3.14. The equation is typically written as C = pi * d = 2 pi * r, where C is the circumference, d is the diameter and r is the radius. The circumference differs from the perimeter in that a perimeter is used to measure geometric figures with straight lines, whereas the circumference measures a continuously differentiable curve.