C = 2\pi r

Thu, 30 Apr 2026 00:54:57 +0000

Understanding the Formula C = 2πr: The Foundation of Circle Geometry When studying circles, one of the most essential formulas is C = 2πr, where C represents the circumference, r is the radius, and π (pi) is a fundamental mathematical constant approximately equal to 3.14159. This elegant equation defines the relationship between a circle’s perimeter and its radius, and it’s a cornerstone in geometry, trigonometry, and engineering. ### What Does C = 2πr Mean? The formula C = 2πr states that the circumference of a circle is equal to two times pi multiplied by the radius. Since the diameter d of a circle is twice the radius (d = 2r), this formula can also be expressed in an easily recognizable form: