This study describes a procedure of using grand canonical Monte Carlo simulations for structural characterization of single-walled carbon nanotube (SWNT) samples. Simulations of nitrogen adsorption were performed on the external and internal surface of homogenous arrays of SWNTs of diameters previously determined from Raman spectroscopy of the samples. The results showed the importance of peripheral grooves on a nanotube bundle and the insensitivity of nanotube diameter towards adsorption on the external surface of a bundle. Simulations also revealed that samples containing thin nanotubes would have less internal and more external adsorption than those comprising of large diameter nanotubes. The total adsorption inside nanotubes could be adjusted by a parameter (between 0 and 1) that resulted in a near perfect fit between simulated and experimental values. This parameter can be interpreted as the fraction of open-ended nanotubes in the sample.