The design of near-surface crown pillars involves the interaction between excavation geometry, rock mass quality, and the in situ stress state. This study proposes a formulation that integrates numerical modeling and empirical criteria to construct a unified framework for stability interpretation. The Modeled Span index is introduced as a hybrid measure that incorporates geometric relationships and the pre-mining stress state, which, when compared with rock mass quality, allows the definition of a probabilistic stability boundary. The results show that the design tool enables the establishment of a consistent classification within the domain represented by the dataset. The Modeled Span chart complements traditional stability assessment approaches and is intended for application in conceptual and prefeasibility studies of crown pillars in Sublevel Open Stoping mining.