A hemisphere is a three-dimensional object formed by half of a sphere and a flat circular base. Any plane that goes through the center of a sphere divides it into two hemispheres.

The radius r of a hemisphere is the segment that connects the center O with any point on the hemisphere. The radius of a sphere is the same as the radius of any of its hemispheres. The volume of a hemisphere with radius r is half the volume of a sphere with radius r. Volume V=2/3π r^3 The surface area of a hemisphere with radius r is the circular flat area plus half the surface area of a sphere with radius r. Surface Area 2 π r^2 + π r^2 =3π r^2