The period T of the motion of an object moving in a circular path is defined as the time it takes to complete one revolution around the circle. The distance travelled during the period is the circumference of the circle = 2*p*r, where r is the radius of the circle. In uniform circular motion the velocity v, is constant, so the general rule that distance = speed * time gives:

T = 2*p*r/v

for uniform circular motion.