Disposable cylindrical shaken bioreactors using plastic bags or vessels represent a promising alternative to stainless steel bioreactors, because they are flexible, cost-effective and can be pre-sterilized. Unlike conventional well-established steel bioreactors, however, such disposable bioreactor systems have not yet been precisely characterized. Thus, the aim of this current work is to introduce a new power input correlation as a potential means to characterize the hydrodynamics of these new systems. A set of rel- evant power input variables was defined and transformed into dimensionless numbers by using the Buckingham’s pi-Theorem. These numbers were then experimentally varied to quantify the relationship among the numbers. A simple correlation was generated for the power input with seven variables. The application of this new correlation was validated using 200 L and 2000 L orbitally shaken bioreactors. In conclusion, the proposed correlation is a useful tool to predict the power input and hydrodynamics during cell cultivation in cylindrical shaken bioreactors of all scales.