Homotopy perturbation method is a novel approach that provides an approximate analytical solution to differential equations in the form of an infinite power series. In this work, homotopy perturbation method has been used to evaluate temperature distribution, efficiency and effectiveness of straight fins exposed to convection. The fin efficiency and the fin effectiveness have been obtained as a function of thermogeometric fin parameter. The results have revealed that the homotopy perturbation method is a very effective and practical approach for a rapid assessment of physical systems. The resulting correlation equations can assist thermal design engineers for designing of straight fins with both constant and temperature-dependent thermal conductivity.