The methodology described for determining stoichiometric factors for Pt clusters has been successfully generalized to 3 other fcc metals, Pd, Ir, and Rh. The use of this model clearly explains the fundamental reason for overstoichiometries experimentally observed on small particle sizes, and is related to multiple adsorption sites whose relative proportions are strongly size sensitive. The model can also be easily adapted to other shapes, provided that the surface statistics are known. The systematic use of this model for determining metallic specific surface areas from chemisorption experiments is therefore highly recommended for the accurate and meaningful calculation of turnover frequencies (TOF), which is one of the most important parameters to be determined in catalysis. We are currently investigating this aspect in our lab.