Green chemistry metrics convert qualitative sustainability principles into quantitative measures that can guide reaction design, route selection, process development, and industrial improvement. This chapter examines atom economy, E-Factor, process mass intensity (PMI), reaction mass efficiency, carbon efficiency, composite scoring approaches such as DOZN 2.0, and life-cycle assessment. Worked examples show how stoichiometry, yield, solvent demand, work-up materials, and route-level losses influence apparently simple efficiency calculations. Industrial comparisons illustrate why solvent and water use frequently dominate material intensity in fine-chemical and pharmaceutical manufacture, while theoretical metrics such as atom economy remain valuable for early route screening. The chapter also explains the limitations of single metrics and the need to interpret mass-based indicators together with hazard, energy, resource, and life-cycle information. Used collectively, these tools provide a practical basis for benchmarking processes, identifying high-impact interventions, and embedding measurable sustainability criteria into chemical design.
Keywords:atom economy, E-Factor, process mass intensity, reaction mass efficiency, DOZN 2.0, life-cycle assessment