Examples can include a system for auto-dimensioning part assemblies in REVIT or other software. A plugin can receive an identifier of a part assembly that is displayed on a graphical user interface (“GUI”). The plugin can determine a dimensioning rule based on the part identifier and dynamically select first and second reference points based on the dimensioning rule. Based on these rules, the plugin can calculate a dimension represented by the first and second reference points. This can include measuring a distance different than the distance between the first and second reference points. Then, the system can display the dimension outside a boundary of the part assembly.