What is the length of an arc which subtends angle θ (degrees) at the centre in a circle of radius r?
(πrθ)/180
For an angle of 360∘ subtended at the centre, the arc length is nothing but the circumference of circle that is 2πr where r is circle radius. For an angle of θ, the arc length will be θ360×2πr =θ180×πr.