If you are asking for the circumference of an arc (definition of arc is "a part of the circumference of a circle or other curve"), then the formula is:
x/360*r*2pi, where x is the angle in degrees and r is the radius.
note that if you want to find the circumference of the sector, the formula becomes
x/360*2*2pi + 2r,
where x is the angle in degrees and r is the radius.
