In the BioFlux software, the user inputs the desired shear stress under which to run the experiment. From this input value, there are equations used to populate the other fields visible to the user. These equations calculate values for shear stress, volumetric flow rate, run time and pressure. In order to apply the correct amount of air pressure to the plate, and thus apply the correct shear, the equations must factor in the correct viscosity of the fluid. The viscosity of a fluid describes its resistance to flow. In the BioFlux software, this value is entered in the Fluid Properties manager. A number of commonly used fluids are preset in the software, such as water and PBS. Custom fluids (and their viscosities) can also be entered in the Fluid Properties module. This technical note will describe some of the important aspects of viscosity and serve as a guide for planning experiments in the BioFlux system.