Plugging the values into our equation for arc length gives us. Find the radius r of that circle. If the measure of the arc or central angle is given in radians then the formula for the arc length of a circle is.
Radius of the arc th.
Calculate the perimeter of a semicircle of radius 1. The arc length is some portion of the circumference. Arc Length Formula All this means is that by the power of radians and proportions the length of an arc is nothing more than the radius times the central angle. Radian Arc-Length Formula Given a circle of radius r and a central angle in radian let L length of the arc cuts off by the angle then L r An angle based at the center of a circle is called a central angle.