What is Circumference?
The Circumference Calculator finds the perimeter (circumference), area, and diameter of a circle from its radius. These are among the most frequently needed geometric calculations in math, engineering, construction, and everyday life.
Circumference is the distance around a circle. It equals 2πr (or πd), where π (pi) ≈ 3.14159. This formula is used everywhere — from measuring wheel rotations to calculating the length of circular fences, pipes, tracks, and pizza crusts.
Real-world applications: tire circumference determines how far a car travels per wheel rotation, pipe circumference determines the amount of insulation needed, and circular track length determines running distances.
Formula
Circumference = 2πr = πd Area = πr² Diameter = 2r
Where: π ≈ 3.14159265 r = radius d = diameter
Examples: Radius 5 → C = 31.42, A = 78.54, d = 10 Radius 10 → C = 62.83, A = 314.16, d = 20 Radius 1 → C = 6.28, A = 3.14, d = 2
How to use this Circumference Calculator?
1. Enter the radius of the circle. 2. See circumference, area, and diameter.
If you know the diameter instead: radius = diameter / 2. If you know the circumference: radius = circumference / (2π).