This study develops and validates a measure that captures the perceived psychological boundary between consumers and brands, which is defined as consumers’ perceived demarcation between themselves and a brand. This construct captures both consumers’ separateness from and relatedness to a brand. A seven-point Venn diagram, which has been proved effective and valid in interpersonal relationship and other self-expansion studies, is applied to measure consumers’ perceived boundary with various brands. The reliability and validity of the boundary measure are assessed with 44 brands. This study finds that consumers’ boundary with brands is significantly correlated with brand-related consumer responses. The discriminant validity and convergent validity between the boundary and self-brand connection, self-brand attachment, and BESC scales are validated. Masculinity incongruence and femininity incongruence between consumers and brands are shown to have a significantly negative relationship with boundary, thus supporting the concurrent validity. In a nomological network, a significant mediation effect of boundary on the relationship between brand-consumer gender identity incongruence and brand-related consumer responses is observed.