Today, many companies have introduced an ERP system - an enterprise resources planning - in order to improve corporate credibility through transparent management and for quick responses to market situations through quick decision making. After the construction of an ERP system, many companies are having difficulty in calculating the appropriate number of personnel required for running the system because of a lack of standard for doing so, as well as a lack of pertinent procedures. As a result, the companies are having to resort to a trial-and-error approach. Therefore this paper studied a model for calculating the appropriate number of personnel required for efficiently running an ERP system after its construction, as well as for constantly meeting its performance targets. The developed model was applied empirically to calculate an appropriate number of personnel required, and an organization was set up according to this. Therefore, the purpose of this study was to present an optimized model for calculating the number of personnel required for operating an ERP system, that which addresses problems of existing models, in order to help companies organize the operation personnel and its size, as well as to provide more objectivity to the calculated number of personnel required and to improve credibility.