Tetrahedral volume = 1/3 (bottom area) * high

If the volume of the parallelepiped corresponding to the volume of the tetrahedron is Pv, the volume of the tetrahedron (Tv) = Pv/6

(x1, y1, z1) is the vertex P

(x2, y2, z2) is the vertex Q

(x3, y3, z3) is the vertex R

(x4, y4, z4) is the vertex S.