We introduce the mode-area probability density function (MA-PDF) as a powerful tool to study transverse Anderson localization (TAL), especially for highly disordered optical fibers. The MA-PDF encompasses all the relevant statistical information on TAL; it relies solely on the physics of the disordered system and is independent of the shape of the external excitation. We explore the scaling of the MA-PDF with the transverse dimensions of the system and show that it converges to a terminal form for structures considerably smaller than those used in experiments, hence substantially reducing the computational cost to study TAL.