Abstract A graphical method to determine the thermal conductivity of particulate composites is presented. In this paper particulate composites sonsist of two solid-solid isotropic phases with the dispersed phase having a constant shape. In the literature there are a large number of micromechanical formulae to estimate the steady-state thermal conductivity. These formulae are based on knowledge of constituent properties and details of the microstructure (i.e. size, shape and spatial distribution of the particles). It is shown with the aid of experimental data that good estimates for the thermal conductivity of commercial particulate composites may be obtained using formulae developed for a microstructure having a random dispersion of equi-sized spheroids.