Using Radius
\(A = \pi r^2\) where \(\pi \approx 3.14159\)
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Circle Area Calculator
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Circle Area Formula
The area of a circle can be calculated using either the radius or diameter.
Key Points:
- The radius is half the diameter
- π (pi) is approximately 3.14159
- Area is always in square units
- The formula works for circles of any size
\(A = \pi r^2\)
Worked Examples
Using Diameter
\(A = \pi (\frac{d}{2})^2 = \frac{\pi d^2}{4}\)
Example: Radius 5 units
\(A = \pi \times 5^2 = 25\pi \approx 78.54\) square units
Example: Diameter 10 units
\(r = 5, A = \pi \times 5^2 \approx 78.54\) square units