© 2023Cloud height is known as the height of the interface that forms between liquid-rich and solid-rich parts of a stirred tank at high solids concentrations. Formation of cloud height is undesired as mixing between the two parts is poor. This poses a significant problem for solid catalyzed reactions as the liquid-rich part is unreacted reactant. To eliminate the cloud height, first, its definition must be clarified and the conditions under which it occurs must be determined. The current definition of the cloud height does not contain the limits of two parameters that significantly affect formation of the cloud height: solids concentration (XV) and impeller speed (N). The definition is also not clear and sufficiently detailed to be applied accurately, causing different interpretations by different researchers. In this study, the aim was to clarify the definition of cloud height by determining the measurement point and the limits of XV and N on cloud height. The majority of the results were obtained in a tall tank (H = 1.5 T) agitated with a 45° down-pumping PBT. For this geometry used, the measurement point was determined as the maximum point solids can reach, which is in front of the baffle, and a meaningful cloud height data can be obtained above 2 vol % and N = 0.32 Njs.