Enter a circle radius and central angle in degrees to calculate arc length.
Cross-check radians, chord, sagitta, circumference share and sector area from the current radius and angle.
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Keep linear inputs in a consistent unit, verify that side lengths or coordinate points can form the stated shape, and treat sketches as explanatory unless explicitly marked to scale. Coordinate formulas can become unstable for nearly degenerate shapes, so invalid or nearly collinear inputs are rejected rather than silently returning misleading values.
Use the interactive product above first. These notes add interpretation, verification and limits below the results and product controls.
Arc length is rθ when θ is measured in radians. If the input is degrees, convert it with θ×π/180 first; mixing degrees directly into the radian formula can make the answer wrong by a large factor.
A measurement labeled across the full circle is a diameter, not a radius. Divide diameter by two before using an arc-length formula and keep the chosen unit consistent for every geometric result.
A full circle has circumference 2πr. The arc should equal the same fraction of that circumference as the central angle is of 360°, which gives a quick independent check for both angle and radius entry errors.
Roads, pipes, drawings and physical edges can deviate from an ideal circle. Use this result when a constant-radius circular model is appropriate; otherwise measured polyline length or a fitted curve may better represent the object.
WebToolArc