What makes a norm strong? Its strength depends not only on the level of agreement about its content (consistency) and its ability to predict behaviour (accuracy), but also on how clearly that content is defined (specificity). This study focuses on the strength of the fairness norm, specifically its specificity, using data from the European Social Survey. I apply Hierarchical Multidimensional Scaling to quantify the cognitive differentiation between merit-based and non-merit-based considerations, providing a direct measure of norm specificity. The results reveal a clear regional pattern: Nordic societies exhibit high fairness norm specificity, with sharply defined categories, while post-communist societies show low specificity, with more ambiguously bounded categories. This variation is negatively associated with the prevalence of rule violations, linking norm specificity to institutional integrity. Crucially, this relationship is distinct from general cultural tightness–looseness, demonstrating that fairness norm specificity operates as a domain-specific phenomenon. By shifting attention from normative content to normative architecture, the study identifies specificity as a measurable dimension of norm strength and highlights how clarity in normative boundaries shapes social coordination and enforcement.