This work presents a novel semi-empirical model for estimating the permeability and inertial coefficient of pin-fin heat sinks that are set as porous media. The forms of correlations for the permeability and inertial coefficient of pin-fin heat sinks are firstly derived theoretically, then a series of pressure drop tests are performed for modifying those correlations. The variable parameters of pin-fins studied herein are the relative longitudinal pitch, the relative transverse pitch, the relative fin height and the relative fin length. The present correlations are reasonable by comparing with the data of other tests. Additionally, within the range of Reynolds number (Re-d = 676-11,252), at a given Re-d, the effect of the relative fin height on the pressure drop is negligible. The pressure drop declines as the relative fin length increases, especially as the relative transverse pitch and the relative longitudinal pitch increase. It increases as the relative transverse pitch declines or the relative longitudinal pitch increases. (c) 2005 Elsevier Ltd. All rights reserved.