When most commercial clusters had one processor core each, decreasing the runtime meant executing the application over more nodes – the associated cost (in $) would scale linearly with the number of nodes. However with the recent advances of multi-core processors the execution time can be increased by utilizing more nodes or by utilizing more cores in the same nodes. In the industrial cluster environments a key question is how to run the applications, to minimize the total cost while maximizing the throughput and solution times of the individual jobs. The number of core used and their contribution to the total runtime reduction is especially interesting since companies often use commercial software that is licensed per year and process. The annual license cost of one single process is often far greater than that of a complete cluster node including maintenance and power. In this paper we present a metric for the calculation of the optimal way to run an application on a cluster consisting of multi-core nodes in order to minimize the cost of executing the said job.