Process capability indices, Cp, Cpk, and Cpm, are well-known indices used widely in the manufacturing industry for measuring process reproduction capability according to manufacturing specifications, but limited to cases with single engineering specification. Therefore, for processes where the quality characteristic is the location relative to a specific location, they can not provide an effective measure. In this paper, we propose a process loss index LG to evaluate the process capability for this issue. Based on the index, we provide the corresponding transformation for production yield. In addition, we tabulate some critical values for process loss index LG to judge if the process capability is capable. The proposed method is useful for the practitioners to measure the process loss and determine whether a process meets the present process yield requirement.