Circle Area Calculator
Compute the area of a circle from its radius: A = π × r².
Calculator
Use the Circle Area Calculator
Result
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Formula
A = π × r²
Step-by-step
- 1
Enter the radius
Distance from center to edge.
- 2
Read the area
Area in square units.
Worked example
Example input: a: 5
Result: 78.5398
Related tools
- Circumference Calculator
2 × π × r.
- Sphere Volume
3D counterpart.
Frequently asked questions
What is the formula for the area of a circle?
A = π × r². For a radius of 5, that is π × 25 ≈ 78.54 in squared units.
What if I only know the diameter?
Halve it first: radius = diameter ÷ 2. A diameter of 10 means a radius of 5 and an area of about 78.54.
Why does π appear in the area formula?
π ≈ 3.14159 is the fixed ratio between the distance around a circle and its diameter — the same for every circle. In area terms that constant shows up as πr².
How do I find the radius from an area?
Work the formula backwards: r = √(A ÷ π). For an area of 50.24 square units that gives √(50.24 ÷ 3.14159) ≈ 4 units of radius. This calculator goes the other direction — enter any radius and it returns A = πr².