Learn how to calculate the circumference of a circle using different formulas and a calculator. Find the radius, diameter, area and circumference of a circle given any one value. Perimeter of the circle is the enclosing boundary of the circle . The area of the circle is the space in a two-dimensional plane covered by a circle . This circle perimeter calculator finds the perimeter (p) of a circle if you know its radius (r) or its diameter (d), and vice versa. Define Circle Formulas Circle formulae are basic formulas of circles in geometry. The formula for calculating a circle 's circumference , or perimeter , is C = πd or C = 2πr, where "d" is the diameter and "r" is the radius. The formula A = πr2 represents the area of a circle , which is the region contained by its circumference . "r" is the radius.
