Enter any one known value of a circle and instantly get the radius, diameter, circumference, and area.
This tool computes all key measurements of a circle, radius, diameter, circumference, and area, from any single known value.
Diameter equals two times radius. Circumference equals two times pi times radius. Area equals pi times radius squared.
Select which value you know from the dropdown, enter that value, and click Calculate to see all other measurements.
Example: For a circle with radius 7, the diameter is 14, circumference is approximately 43.98, and area is approximately 153.94 square units.
What is the value of pi used. This tool uses the precise JavaScript value of pi, approximately 3.14159265358979.
Can I calculate from the area. Yes, selecting area as the known value back-calculates the radius using the square root of area divided by pi.