IEC 62610-6:2020 deals with thermal management for cabinets in accordance with IEC 60297 and IEC 60917 series, provides compatible measurement methods of recirculation ratio and bypass ratio which are indicators for defining quality of airflow in the forced air cooling that can be commonly applied to indoor cabinets for mounting subrack and/or chassis-based equipment. This document contains the following: a) the definition of recirculation and bypass flow rates in the cooling of the cabinet, b) the levels of the recirculation ratio RC, c) the definition of the formula for the recirculation ratio RCs of forced air cooling subrack and/or chassis-based equipment installed in the cabinet, d) the definition formula of recirculation ratio RCr and bypass rate BPr of the entire cabinet, e) the requirements of the measuring method of each temperature necessary for calculating the recirculation ratio RCs, RCr and bypass ratio BPr. The purpose of this document is to provide: • for the equipment integrator and development designer of the cabinet the criteria for efficiently and correctly determining the specification, and • for the supplier of the cabinet the measuring and classifying method for the airflow recirculation rate of the subrack and/or chassis-based equipment installed in the cabinet.