Reviewed by CalcMulti Editorial Team·Last updated: ·← Geometry Hub
The area of a circle is A = πr², where r is the radius (the distance from the center to the edge). π (pi) ≈ 3.14159265. The formula tells you the number of square units that fit inside the circle.
You can calculate circle area from the radius, diameter (d = 2r), or circumference (C = 2πr). This calculator accepts any of the three inputs and converts automatically.
Example: a circle with radius 5 cm has area A = π × 5² = π × 25 ≈ 78.54 cm². The same circle has diameter 10 cm and circumference ≈ 31.42 cm.
A = π × r²
| Radius | Diameter | Area (πr²) | Circumference (2πr) |
|---|---|---|---|
| 1 | 2 | 3.14 | 6.28 |
| 2 | 4 | 12.57 | 12.57 |
| 3 | 6 | 28.27 | 18.85 |
| 4 | 8 | 50.27 | 25.13 |
| 5 | 10 | 78.54 | 31.42 |
| 6 | 12 | 113.10 | 37.70 |
| 7 | 14 | 153.94 | 43.98 |
| 8 | 16 | 201.06 | 50.27 |
| 10 | 20 | 314.16 | 62.83 |
| 12 | 24 | 452.39 | 75.40 |
| 15 | 30 | 706.86 | 94.25 |
| 20 | 40 | 1256.64 | 125.66 |
½ × base × height, Heron's formula, two sides + angle
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This calculator is for educational purposes only and does not constitute professional advice. Results are based on standard mathematical formulas. Always verify critical calculations with a qualified professional before making important decisions.