⭕ Circumference Calculator
Calculate circle circumference and area
How Circumference Is Calculated
Formula
C = 2πr = πd
- 1Enter the radius or diameter of the circle.
- 2If diameter is given, radius is calculated as r = d/2.
- 3Circumference is calculated as C = 2πr.
- 4Area is calculated as A = πr².
- 5Both the radius and diameter are shown for reference.
About Circumference Calculator
Calculate the circumference and area of a circle from radius or diameter. Shows C = 2πr and A = πr² formulas with step-by-step breakdown.
Frequently Asked Questions
What is circumference?
Circumference is the distance around the outside of a circle — its perimeter. It equals π times the diameter, or 2π times the radius.
What value of π is used?
This calculator uses JavaScript's built-in Math.PI, which is accurate to about 15 decimal places: 3.141592653589793.
How do I find circumference from area?
First find the radius: r = √(A/π). Then calculate C = 2πr.