Two types of biomass solid particles, elephant grass ("Pennisemm purpureum Schum." variety) and sugarcane trash have been studied in laboratory in order to obtain information about several geometrical properties. In both cases, the length, width, and thickness of fifty randomly selected particles from the fractions of each size class or group of particles, obtained by mechanical fractioning through sieves, were measured manually given their sizes. A geometric model of rectangular base prism type was adopted based on observations. It was demonstrated that most of the measured particles exhibited lengths significantly greater than width (I >> a). From those measurements, average values for other geometrical properties were estimated; for example, shape factor, sphericity, particle specific surface areas, equivalent diameter, etc. A statistical analysis was done, and empirical and semi-empirical mathematical correlation models were proposed. These correlation models were obtained by non-linear regression analysis to describe the characteristic dimension of particle dependence on geometrical properties, which proved to be a good fit for the reported experimental data. (C) 2012 Elsevier B.V. All rights reserved.