Sector area
Sector area: A = πr²·θ/360 in degrees or A = r²·θ/2 in radians; enter the radius and central angle to get the area plus arc length, chord, sagitta and the arc-plus-chord perimeter; an angle beyond 360° or 2π is rejected.
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Result
One quantity per line, ready to copy.
Enter a radius to calculate
What this tool does
- Compute the area and arc length of a fan-shaped panel, pizza slice or blade, and get the chord for cutting.
- Work in radians (for example π/2) when checking maths or code without converting by hand.
- Estimate the rise of an arch from the sagitta and chord when bending pipes.
Example
Input
1
Output
半径 1 的扇形面积：0.785398 弧长 l：1.570796 弦长 c：1.414214 矢高 s（弧中点到弦）：0.292893 弧加弦 l + c：2.98501 长度单位 u，面积 u²，体积 u³
Radius 2 with a 180° central angle: area 2π ≈ 6.283185, arc 2π ≈ 6.283185, chord 4 and sagitta 2. Switching to π rad gives exactly the same numbers.
Frequently asked questions
Degrees or radians?
Switch the unit to radians and the angle is read in rad, so π means 180°. Both modes give identical areas and arc lengths — only the input unit differs, and anything beyond 2π is rejected.
What is the sagitta?
It is the perpendicular distance from the middle of the arc to the chord, s = r(1 − cos(θ/2)). For an arch or a bent pipe it is the rise, and at 180° it equals the radius.
Can the angle be 360°?
Yes — then the sector is the whole circle, the area is πr² and the chord is 0. Anything above 360° (or 2π in radians) is rejected instead of silently wrapping.
Keywords：扇形面积sector area圆心角弧长弧度几何计算