r = 5 cm
- Input
- r = 5
- Expected output
- A = 78.54 cm², C = 31.42 cm
A = π × 25 ≈ 78.54.
circle area calculator
Circle Area Calculator
Circle area is A = π × r², where π ≈ 3.14159. The circumference (perimeter) is C = 2 × π × r.
Why A = πr²
- The formula πr² can be derived by slicing the circle into thin wedges and rearranging them into a parallelogram. The "length" is πr and the "height" is r, so A = πr × r = πr².
Examples
Safe use
- Input
- context + tool result
- Expected output
- interpreted with limits and next steps
Use the result as technical or educational support, keeping the tool limits explicit in the workflow.
Full tool FAQ
Use any unit you prefer (cm, m, inches…). The area/volume will be in the corresponding squared/cubed unit. For example, if you enter cm, area will be in cm².
Frequently asked questions
What is the difference between radius and diameter?
Diameter is twice the radius (d = 2r). To use the diameter, divide it by 2 before entering.
Does this page replace official or professional review?
No. It helps explain the scenario and use the tool more safely, but real decisions should consider official sources, full context and qualified guidance when needed.