Project Setup Wizard Page 2 - Specify Unit Settings

Specifies the base unit for project drawings as imperial or metric.

Specify the Base Unit for Project Drawings
Specifies whether units-based properties are reported in inches or millimeters.
Report Nominal Diameters of Imperial Content In
Specifies whether nominal diameters of imperial content is reported in millimeters or inches. If you select the latter, your project has mixed metrics, that is, even in a metric project, nominal diameters of imperial content are reported in inches.