ObjectVolume
Calculates Volume, Surface Area & Centroid of a Closed Triangular Mesh
...Tetrahedrons with back facing triangles are added and those with forward facing triangles are subtracted yielding the object volume.
A detailed description of the process is presented in the ObjectVolumeTutorial.doc document as well as program logic and results.
A key component in the program is a subroutine that calculates the volume of a tetrahedron. Four sets of equations were tested and to my surprise all four produced similar results in accuracy and timing.