To change the default system of units used

In order to change the system of units used in STAAD.Pro Physical Modeler, do the following.

Select the File ribbon tab. The backstage view opens.
Select Options. The Configuration dialog opens.
Select the Units tab.
Select the Units system you want to use as the default.
(Optional) Select the default unit to use for any of the measurements to customize the configuration of the selected Unit system.
Click OK.

The Unit System is changed in the Status Bar. This will be used as the default unit system for all models as well.

Tip: You can change the unit system from the status bar at any time for the current model, as well.