If you know the length of the radius. This tutorial gives you the semicircle radius formula and explains how to calculate the radius of the semicircle given the circumference or the diameter. The perimeter of a semicircle is p R 2 R which can also be written as R p 2 by factoring out R.
You might think that the perimeter of a semicircle is half the perimeter of the circle.
See Angle inscribed in a semicircle. The circumference of a semicircle is not equal to half of the circle circumference - you need to add also the diameter of the semicircle as another boundary was created. Length of Semicircle arc is given as r. Where R Radius of the semicircle.