A methodology to evaluate the effect of gas pores on fatigue life of aluminium die casts is proposed in terms of stress concentration factor. As observed in many fatigue tests, it is not always the case that the largest sized pore initiates fatigue crack. So we need to consider the interactions between the gas pores based on their configuration, shapes and sizes. Stress concentrations around irregular shaped pores play important roles in fatigue crack initiation and consequent fatigue life. In present study, an empirical formulation of elastic stress concentration factor around a pair of spherical shaped cavities is derived by numerical results of three-dimensional finite element linear elastic analyses. The conclusion can be further extended to understand the stress concentration around irregular shaped clustered gas pores. The effect of inter-pore distance and orientation of inter-pore axis to loading direction, on stress concentration factor, is obtained numerically by systematically changing each of these parameters. Finally, a suitable function is chosen to fit the stress concentration data and its validity is discussed from a mechanical standpoint.