Circle Area Calculator
Find the area of a circle from its radius — instantly and using the exact formula S = π · r².
Formula
S = π · r²
r is the radius of the circle, π ≈ 3.14159.
About the circle area calculator
The area of a circle is the size of the flat region enclosed by its boundary. It depends only on the radius and is found with the formula S = π · r².
The radius is the distance from the center of the circle to any point on its edge. If you only know the diameter, divide it by two to get the radius.
The calculation runs instantly right in your browser — nothing is sent to a server, so everything stays local and private.
Benefits
Instant results
The area updates the moment you enter the radius.
Exact π value
Uses a precise value of π for a reliable result.
Fully private
All math happens locally in your browser with no uploads.
Frequently asked questions
How do I find the area of a circle from the radius?
Square the radius and multiply by π: S = π · r². The calculator handles this automatically.
What is the difference between a circle and its circumference?
The circumference is the boundary line, while the circle is the whole region inside it. Area refers to that filled region.
What if I know the diameter instead of the radius?
Divide the diameter by two to get the radius, then enter that value in the calculator.
What unit will the area be in?
If the radius is in centimeters, the area is in square centimeters (cm²).
Which value of π is used?
The calculator uses a precise value of π (≈3.14159) so the result is as accurate as possible.