Circle Area Calculator

Calculate circle area from radius, diameter, or circumference. Optionally calculate sector area.

Enter an angle less than 360° to calculate sector area

Circle Area Formulas

The area of a circle is the amount of space enclosed within its circumference. It's one of the most fundamental measurements in geometry and is used in countless applications from engineering to everyday calculations.

Key Formulas

  • Area from radius: A = Ï€r²
  • Area from diameter: A = Ï€(d/2)² = Ï€d²/4
  • Area from circumference: A = C²/(4Ï€)
  • Sector area: A_sector = (angle/360°) × Ï€r²
  • Arc length: L = (angle/360°) × 2Ï€r

Note: For precise calculations, this calculator uses the mathematical constant π (pi ≈ 3.14159) rather than approximations. Enter an angle less than 360° to calculate the area of a circular sector (like a slice of pie) and its corresponding arc length.

This calculator provides mathematical calculations for circle area, sector area, and related measurements based on standard geometric formulas. Results are accurate to four decimal places. While we strive for accuracy, please verify important calculations independently. This tool is for educational and informational purposes.

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