This study addresses the challenge of measuring circularity within procurement-to-waste system boundaries, where existing methodologies were deemed inadequate due to their complexity or limited scope. To fill this gap, we propose an extension of the Circularity Mass Utilisation (CMU) Index, currently employed at the EU level, by incorporating circular inflow to better account for procurement decisions. The research culminates in the following formula: CMU Extended = (Circular Inflow + Circular Outflow)/(2 * Total Material Use). Successful testing with SWISS International Air Lines Ltd., using single-use in-flight drinking cups as a case study, demonstrates its practical relevance in the industry and suggests that the approach is likely to be applicable across various sectors beyond the airline industry.