In our previous research, thermal performance investigation of straight fins has been carried out in detail and dimensionless analytical expressions of fin efficiency and fin effectiveness have been presented for the first time in literature via homotopy perturbation method. In this work, previous works have been extended to porous fins. Governing equations have been formulated by utilizing Darcy’s model. Dimensionless temperature distribution along the length of porous fin has been developed as a function of porosity and convection parameters. The ratio of porous fin to solid fin heat transfer rate has also been investigated as a function of thermo-geometric fin parameter. The results have been compared with those of finite difference method for a specific case and an excellent agreement has been obtained. The expressions developed are beneficial for thermal engineers for preliminary assessment of thermophysical systems.