Multilateral trade-policy evaluation and policymaking depends on our continuing efforts to better model economic impacts. Recent innovations link general-equilibrium (GE) and partial-equilibrium (PE) models to capture both economy-wide and product-specific impacts. In this paper we highlight tariff aggregation issues in the context of the Regional Comprehensive Economic Partnership (RCEP). We find that product-specific information on tariffs within the PE-GE structure is superior to either trade weighting or simple averaging techniques applied in pure GE studies.