ISO/TS 11888:2011 describes methods for the characterization of mesoscopic shape factors of multiwall carbon nanotubes (MWCNTs). Techniques employed include scanning electron microscopy, transmission electron microscopy, viscometry, and light scattering analysis. ISO/TS 11888:2011 also includes additional terms needed to define the characterization of scattered bending persistence length (SBPL). Two approximation methods are given for the evaluation of SBPL. Well-established concepts and mathematical expressions, analogous to polymer physics, are utilized for the definition of mesoscopic shape factors of MWCNTs.