The arc length of a circle can be calculated with the radius and central angle using the arc length formula, Length of an Arc = θ × r, where θ is in radian. Length of an Arc = θ × (π/180) × r, where θ is in degree.

To calculate arc length without radius, you need the central angle and the sector area: Multiply the area by 2 and divide the result by the central angle in radians. Find the square root of this division. Multiply this root by the central angle again to get the arc length. The units will be the square root of the sector area units.