Chemisorption of probe molecules such as hydrogen and carbon monoxide on the surface of Pt particles is the most common chemical technique used to estimate the crucial parameters of metal catalysts, namely the dispersion (D), the particle size (d), and the metallic specific surface area (SPt). However, it remains a controversy concerning the stoichiometry of adsorbate per surface metal atom, leading to an inaccurate estimation of D, d, and SPt. A model describing the statistics of the surface atoms and sites on perfect cuboctahedron clusters was developed to assess values of D, d, and SPt, assuming the most favorable adsorption sites based on density functional theory (DFT) calculation of the literature. This model successfully predicted the experimental values of D, d, and SPt determined from H or CO chemisorption data, and it allowed providing a set of simple equations for the accurate determination of these parameters from chemisorption experiments on Pt.