How Do You Determine the Circumference of a Semicircle?

By Staff WriterLast Updated Mar 25, 2020 10:09:08 PM ET

The perimeter of a semicircle is 1/2 of the circumference of the corresponding complete circle plus the diameter of the circle. The distance around the outside of a semicircle is generally called its perimeter.


A semicircle can be seen as the shape that is formed when a circle is cut in half along its diameter. The arc that remains as a part of the semicircle is half as long as the circumference of the whole circle. The perimeter of the semicircle also includes the straight line that connects the two ends of that arc. That line is the same length as the diameter of the original circle.

The perimeter of the semicircle is the length of its arc plus the length of the line that closes the shape and can be calculated using these equations:

P (semicircle) = 1/2 C (circle) + d (circle)

C (circle) = ?d (circle)

d (circle) = 2r (circle or semicircle)


  • C is circumference
  • P is perimeter
  • d is diameter
  • r is radius
  • ? = 3.14