Volume of tetrahedron ABCD = (1/6)|[AB AC AD]|.

Centroid of tetrahedron = (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^3/(6sqrt(2)). Height = asqrt(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.