Enter values and select Calculate to see your result.
Calculate circle area and circumference from radius
Area uses square units and circumference uses the original length unit.
View formula
Area = πr²; circumference = 2πr.
How to use the Circle Calculator
Calculate a circle's area and circumference from its radius.
- Enter the radius.
- Calculate area and circumference.
- Keep units consistent when reusing the result.
Circle Calculator formula
Area = πr²; circumference = 2πr.
Worked example
Inputs: Radius 5 units.
What to expect: Area is about 78.5398 square units and circumference about 31.4159 units.
How to read your result
Area uses squared units while circumference uses the original length unit.
Frequently asked questions
Can I enter diameter?
Convert diameter to radius by dividing by two.
Which pi is used?
The browser's mathematical pi constant is used for the displayed precision.