Despite the fact that aerated stirred tank reactors are widely used in industry and often studied, their design and scale-up still remains challenging. Especially the specific power input is a crucial and geometry-dependent scale-up parameter, usually calculated with the dimensionless power number Po. Within the scope of this study, the power number is measured for different stirrer types and configurations in a laboratory and an industrial-scale aerated stirred tank reactor. Good agreements to literature are found for the unaerated case for the two-stage stirrer configurations at different stirrer spacing for both scales. By literature only the aerated case in the laboratory scale can be predicted. Scale-up of an aerated industrial-scale reactor is challenging because of a specific influence of the aeration. In case of a three-stage Rushton configuration, an asymmetrical distribution of the stirrers should be preferred to ensure a high power number as well as good power performance under aerated conditions.