Composite materials are an integral part of electrical systems; however, the determination of their dielectric properties through calculation is sometimes problematic. The aim of this paper is to demonstrate a way to determine the effective permittivity of a composite material by using a 3D electric field model while exploiting the distribution of electric energy and to verify the results by values obtained experimentally. Two types of samples were investigated: with the inclusion phase evenly distributed across the host phase in one plane and in two planes. The experiment was conducted by means of Tettex 2830/2831, a precise dielectric analyzer for solid and liquid dielectrics and Tettex 2914, a special temperature-controlled electrode system. The computation was performed by COMSOL Multiphysics professional software. The results obtained through a 3D model corresponded to the results of the experiment.