Using Radius
\(A = \pi r^2\) where \(\pi \approx 3.14159\)
円面積計算機
半径または直径から円の面積をステップバイステップの解法で計算
Circle Area Calculator
結果
値を入力して計算をクリックして結果を表示してください。
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