Calculate the area of a circle given its radius or diameter.
Circle Dimensions
Diameter (calculated): 20.00
Calculation Results
314.16
Total Area (A)
The space occupied by the circle in a 2D plane.
Circumference (C)62.83
Diameter20.00
r
πr²
About this calculator
Understanding Circle Area
The area of a circle is the total surface contained within its boundary. It is proportional to the square of its radius. The constant π (pi), approximately 3.14159, represents the ratio of any circle's circumference to its diameter.
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Pro Tips
Radius is the distance from the center to the edge.
Diameter is the distance across the circle through the center (d = 2r).
If you double the radius, the area becomes four times larger (2² = 4).
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Fun Facts
"Pi is an irrational number, meaning its decimal representation never ends or repeats."
"The ancient Babylonians used 3.125 as the value of pi about 4,000 years ago."
"If you cut a circle into many small enough 'pie' slices and rearrange them, they form an approximate rectangle with width r and length πr!"
