Metrics can be used to evaluate the overall structural complexity of the data warehouse (DW) and assess its quality in the early phases of design and development. The requirements data model plays a crucial role in developing a quality-based DW. Several researchers have assessed the quality of the requirements data model using the requirements metrics based on the agent-goal-decision-information (AGDI) model, both formally and empirically. However, no assessment has been implemented on the structural complexities of the requirements data model based on goal, decision, and information hierarchies. Considering this, the study proposes a novel structural complexity metric to assess the overall complexity of the requirements data model at different phases (information, decision and organisation) and to analyze the links between the different levels of granularity in these models. The proposed metric is formally validated by applying the measurement theory-based Briand’s framework for complexity measure (i.e., one of the five notions of measurements in Software Engineering) by confirming that the proposed metric is valid and defined correctly under certain mathematical properties. As a result, we conclude that the proposed structural complexity metric is accurately defined and effectively valid. We also provide a detailed comparison of various requirements metrics commonly used in similar contexts to contextualize our proposed metric within the broader landscape of existing methodologies. Additionally, we have included comprehensive guidelines and practical examples for applying the proposed structural complexity metric in DW development scenarios to enhance its utility among practitioners. The proposed metric can be utilized to ensure the accuracy of the requirements model, thereby improving the overall quality of DW.