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Circle Calculator
Calculate a circle from its radius, diameter, area or circumference. Explore central-angle arc and sector measurements, or calculate a circular segment with its chord and sagitta.
How do you calculate a circle?
For radius r, diameter is 2r, circumference is 2πr and area is πr². For a central angle θ in radians, arc length is rθ and sector area is r²θ/2. This calculator converts an entered angle in degrees to radians for those formulas.
Frequently asked questions
How do you calculate a circle?
For radius r, diameter is 2r, circumference is 2πr and area is πr². For a central angle θ in radians, arc length is rθ and sector area is r²θ/2. This calculator converts an entered angle in degrees to radians for those formulas.
Are my measurements uploaded?
No. The formulas run in this browser and this tool does not upload or save your measurements.
What are the area and circumference of a circle with radius 1?
The area is π (about 3.14159) and the circumference is 2π (about 6.28318). Results are rounded for display.
How do I calculate arc length?
Multiply the radius by the central angle in radians. This tool accepts degrees and converts them before calculating.
What is the difference between a sector and a segment?
A sector is bounded by two radii and an arc. A segment is bounded by a chord and its arc; its area is calculated here from the central angle.