Скачать или смотреть How to change Units in Revit And Background

Open the Manage Tab: In the Revit ribbon, go to the Manage tab.
Access Project Units: In the Settings panel, click on Project Units.
Select a Discipline: In the Project Units dialog box, choose the relevant discipline (such as "Common," "Electrical," or "Structural").
Choose Unit Type: Find the unit you want to change (e.g., "Length") and click on its value in the Format column.
Specify Units: In the Format dialog, select your desired units (e.g., meters, millimeters, or feet and inches) from the dropdown menu.
Adjust Settings (Optional):
Rounding: Set the desired rounding for your measurements.
Unit Symbol: Choose to display or suppress the unit symbol.
Display Options: Use options like "Suppress trailing 0's" or "Suppress 0 Feet" to control how numbers are displayed.
Apply Changes: Click OK in the Format dialog, and then OK again in the Project Units dialog to save your changes.