Circle Calculator
Calculate radius, diameter, circumference, and area of a circle. Enter any one variable to instantly solve for the other three using standard geometric formulas.
Circle Geometry Definitions
- Radius (r): The distance from the center of the circle to any point on its edge.
- Diameter (d): The distance across the circle passing through the center. It is exactly twice the radius ($d = 2r$).
- Circumference (C): The total distance around the outside of the circle (perimeter).
- Area (A): The amount of 2D space inside the circle.
- Pi ($\pi$): A mathematical constant approximately equal to 3.14159. It represents the ratio of a circle's circumference to its diameter.
? Frequently Asked Questions
Pi (π) is the ratio of a circle's circumference to its diameter. Regardless of the circle's size, this ratio is always approximately 3.14159.
Divide the area by Pi, then take the square root of the result. Formula: r = √(A / π).
Yes. If you enter inches, the results are in inches (and sq inches for Area). If you enter meters, the results are in meters (and sq meters for Area).