# arc

An arc is any part of a curved line or part of the circumference of
a circle; the word comes from the Latin *arcus* for a bow, which also gives rise to "arch". **Arc length** is the distance along part of a curve.

For a circle of radius *r*, the length (*s*) of an arc covering *θ* degrees on that circle is given by

*s*= 2

*r*× π ×

*θ*/360.

If the angle is measured in radians the length
of the arc is given by the product of the radius and the angle, i.e., *s* = *r θ*. The arc is said to subtend the angle *θ* at the center of the circle.