The steady-state thermal response of solid materials is controlled by their thermal conductivity. For porous materials, the local thermal conductivity is difficult to use in the characterization of the overall thermal response and therefore, often, the concept of effective thermal conductivity that depends on the porosity is used. In this work, two methods for computing the effective thermal conductivity of porous materials are studied. The first approach uses an image-based approach where a stack of 2-dimensional images are used to build a three-dimensional structure with porosities. The effective thermal conductivity of this structure is then calculated using the finite element software ABAQUS. The second approach, known as Maxwell's method, is used on a medium consisting of spherical pores arranged in various configurations such as simple-cubic, body-centered cubic and face-centered cubic arrays. Results from the numerical simulations and the applicability of the two approaches to structures with complex porous structure are discussed. The effect of porosity on the effective thermal conductivity is also discussed.