Volume of tetrahedron ABCD = $\frac{1}{6}$|[AB AC AD]|.

Centroid of tetrahedron = $\frac{A+B+C+D}{4}$ (average of all four vertices).

Opposite edges of a tetrahedron: (AB, CD), (AC, BD), (AD, BC). In a general tetrahedron, opposite edges need not be equal or perpendicular. An isosceles tetrahedron has all opposite edges equal.

For a regular tetrahedron with edge a: Volume = a^$\frac{3}{6*sqrt(2}$). Height = a*sqrt$\frac{2}{3}$. The centroid divides each median in ratio 3:1.

The four faces of a tetrahedron are triangles. The sum of the vector areas of the four faces (with outward normals) is zero: this is the vector analog of a closed surface having zero net flux in the absence of sources.