This article describes a novel approach for deciding optimal horizontal extent of soil domain to be used for finite element based numerical dynamic soil structure interaction (SSI) studies.SSI model for a 12 storied building frame,supported on pile foundation-soil system,is developed in the finite element based software framework,OpenSEES.Three different structure-foundation configurations are analyzed under different ground motion characteristics.Lateral extent of soil domain,along with the soil properties,were varied exhaustively for a particular structural configuration.Based on the reduction in the variation of acceleration response at different locations in the SSI system (quantified by normalized root mean square error,NRMSE),the optimum lateral extent of the soil domain is prescribed for various structural widths,soil types and peak ground acceleration levels of ground motion.Compared to the past studies,error estimation analysis shows that the relationships prescribed in the present study are credible and more inclusive of the various factors that influence SSI.These relationships can be readily applied for deciding upon the lateral extent of the soil domain for conducting precise SSI analysis with reduced computational time.