Overview
A circle is the set of points at the same distance from a center. That distance is the radius, and the diameter is twice it. A circle's circumference and area relate to the radius through π, which appears in every circle calculation.
Formula
Diameter = 2r, circumference = 2πr, area = πr².
How it works
Enter the radius
Use a positive value in the same measurement unit.
Compute the diameter
Multiply the radius by 2.
Compute the circumference
Multiply 2 × π × radius.
Compute the area
Multiply π by the radius squared.
Worked examples
Example 1: radius 5
Diameter 10, circumference ≈ 31.4159, area ≈ 78.5398.
Example 2: radius 2.5
Diameter 5, circumference ≈ 15.7080, area ≈ 19.6350.
Frequently asked questions
Is the area in square units?
Yes. If the radius is a length unit, the area is in that unit squared.
How do I find the radius from the circumference?
r = circumference ÷ (2π).
What is the difference between circumference and area?
Circumference is the length of the outer boundary, while area is the space inside the circle.
This calculator is for educational and informational purposes only and is not a substitute for professional advice.