Circle Calculator – Circumference, Area & Arc Length
Circle & Circular Sector Calculator C = 2πr
Enter the radius or the diameter. Add a central angle (degrees or radians) to also get the arc length and the sector area. Each result is shown with π and as a decimal rounded to 3 places.
The calculator above computes the circumference and area of a circle, and the arc length and sector area for a given central angle.
Formulas used
C = 2πR, S = πR²
Arc length l = πRn / 180 (n in degrees)
- Sector area = l·R / 2.
Worked example
R = 5:
C ≈ 31.42, S ≈ 78.54
Enter the same values in the calculator above to see every step of the solution.
How to use the calculator
- Enter the radius (or diameter) and, optionally, the central angle.
- Press the calculate button. The result appears instantly.
- Read the step-by-step solution, rendered with KaTeX, to check your own work.