In semi-batch or continuously stirred reactors, often a feed containing one or more reactants has to be mixed with the contents of the vessel. For fast competitive or consecutive reactions the mixing rate of the feed stream with the vessel contents has a large influence on the product quality. The mixing rate is often controlled by the turbulent dispersion process. Therefore, it has been suggested in the literature to keep the turbulent dispersion time constant upon scale-up to obtain a constant product quality. In this study, based on a combination of a theoretical model, Planar Laser Induced Fluorescence experiments and Laser Doppler Velocimetry experiments, the turbulent dispersion coefficient is determined. This has been done for the case that a feed stream is mixed in a stirred vessel by a combination of feed stream and stirrer generated turbulence. The turbulent dispersion coefficient is used to derive an equation for the turbulent dispersion time as function of several design and process variables.