Advancing circularity metrics: Revisiting the Ellen MacArthur Foundation’s Material Circularity Indicator

Circularity metrics simplify complex systems, and trade-offs between simplicity, scope, and usability introduce unavoidable limitations. We revisit the Ellen MacArthur Foundation’s Material Circularity Indicator (MCI) to identify opportunities for a more accurate, comprehensive, reliable measure of circularity. Although widely used and highly regarded, the MCI exhibits limitations and methodological weaknesses. Specifically, it adopts problematic modeling choices, including a single-cycle view that overlooks nonlinear, multi-cycle retention benefits, an oversimplified 50:50 waste-allocation rule, and insufficient differentiation between internal and external recycling streams. We propose a readily implementable correction to the 50:50 rule and show that its errors can exceed 2000%. In addition, we note broader limitations of the MCI, including insensitivity to energy requirements, infrastructure and equipment burdens, material quality degradation, and its limited alignment with wider economic and environmental impacts. Building on these findings, we outline desiderata to guide the development of more accurate, comprehensive, and reliable circularity indicators.