As such, there are no units in AutoCAD, there are conventional units and each user himself implies the necessary dimension of these conventional units (mm, cm, m, inch, foot) when creating objects in the AutoCAD document.
However, you might want to insert objects from one document into another document, and document users created objects in them in different unit conventions (for example, one in millimeters of the other in inches). For the correct result when inserting objects from such documents it is necessary to perform scaling. The scale value depends on the physical meaning of the conventional unit of measurement, and it is set in the Format menu item Units.
In the insert Scale drop-down list, select the units in which objects are created in the current document.
The user can himself at any time pre-scale objects to the required units using the SCALE command (_scale). The magnitude of the scale depends on what units of measurement in which you want to convert. For example, to convert from millimeters to inches, the scale factor would be 0.03937.
You can also use the-DWGUNITS command to adjust the units and scale to the selected units.