Calculations at a semicircle. Radius and diameter refer to the original circle, which was bisected through its center. Enter one value and choose the number of decimal places. Then click Calculate.

Formulas:
d = 2 r
a = π r
p = π r + 2 r
A = π r² / 2

pi:
π = 3.141592653589793...

Radius, diameter, arc length and perimeter have the same unit (e.g. meter), the area has this unit squared (e.g. square meter).

radius of the original circle

diameter of the original circle

arc length

perimeter p, area A

The semicircle is axially symmetrical to its bisector, but neither point-symmetrical nor rotationally symmetrical. A semicircle is both a circular-segment and a circular sector with an angle of 180 degrees. A halved annulus is a semi-annulus. The three-dimensional equivalent of the semicircle is the hemisphere; extended straight into the third dimension it forms a half cylinder. Many of the shapes on this page are based on the semicircle. The stadium has a rectangle between two halves of a circle. The simple heart shape places two semicircles on adjacent sides of a square. The claw is created when a smaller semicircle adjacent to one side is subtracted from a larger one, similar to the arbelos, where another semicircle is removed on the other side. A salinon is made from four semicircles, two of which are the same size. A bulge is a semicircle that sits on quarter circles that bend outwards. And a polycircle is an equilateral polygon with a matching semicircle on each side. If you subtract a semicircle half the size of a claw from the inside of a semicircle and add the removed piece with the straight side to the remaining straight side of the original semicircle, you get half a yin-yang symbol, which has the area of a semicircle but the circumference of a circle.