The minimum cross diameter of organic species is highly important in catalyst and adsorbent design. In the aromatics industry, the size of the desired compound is the cornerstone of the commonly known shape-selective processes. In spite of the paramount importance of the said sizes, information in the literature is scarce and inconsistent. A thorough methodology was developed using the commercial software ChemBio3D Ultra. The minimum cross diameter of 21 aromatic compounds was calculated including benzene, toluene, ethylbenzene, xylene isomers, ethyltoluene isomers, diethylbenzene isomers, ethylxylene isomers, and trimethylbenzene isomers.