FLUENT provides four built-in unit systems: British, SI, CGS, and "default.'' You can convert all units from one system to another in the Set Units panel (Figure 5.3.1), using the buttons under the Set All To heading.
To choose the English Engineering standard for all units, click on the british button; to select the International System of units (SI) standard for all units, click on the si button; to choose the CGS (centimeter-gram-second) standard for all units, click on the cgs button; and to return to the "default'' system, click on the default button. The default system of units is like SI, but uses degrees instead of radians for angles. Clicking on one of the buttons under Set All To will immediately change the unit system. You can then close the panel if you are not interested in customizing any units.
Changing the unit system in the Set Units panel causes all future inputs that have units to be based on the newly selected unit system.