Sector Area
Enter the radius and the central angle.
Result
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Enter numbers to see the result.
Arc length
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Fraction of circle
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Formula: Sector area = (1/2) r^2 theta, with theta in radians. Arc length = r x theta.
Find the area of a circle sector from the radius and the central angle, plus the arc length.
Enter the radius and the central angle.
Enter numbers to see the result.
A sector is a slice of a circle, and its area is (1/2) r^2 theta, where theta must be in radians. The tool converts degrees for you. A 90-degree sector of radius 5 has area (1/2) x 25 x (pi/2), about 19.63.
The same angle gives the arc length: r x theta. Together, area and arc length describe the whole slice, which is handy for problems about pizza slices, pie charts, and circular segments in design work.