Can the radius be zero?
Yes. A zero-radius circle has zero diameter, circumference, and area.
Circle Calculator
Calculate diameter, circumference, and area from a circle radius.
Calculations happen locally. We do not send your values to our server.
Example
A circle with radius 10 has diameter 20, circumference about 62.8319, and area about 314.1593.
Calculation method
Diameter equals 2r, circumference equals 2πr, and area equals πr² using the browser’s full available value of π.
Important notes
Results are mathematical estimates displayed with rounded decimals; area is expressed in square units.
Frequently asked questions
Which unit does the answer use?
Diameter and circumference use the radius unit, while area uses its squared unit.
Can I enter a diameter instead?
Convert it to a radius by dividing the diameter by two before entering it.