Autodesk Inventor – Change Units

 Options panel  Document Settings and then select the Units tab in the dialog box. Select the Length drop-list to change units such as inches to mm. When you change the units setting, all existing values in the file display as the new units. All subsequent entries are displayed in the new units. Unit value settings are saved with the file.

You can also override the default units in any value box. For example, you can type 12mm in the dimension value box of a file using an inch unit of length. The result is displayed as 0.472, but the original 12mm unit value is retained and appears in the value box when you edit.