Click File > Properties.
On the Properties dialog box, click the Units tab. You can set the units for the length, area, or angle of a drawing.
This setting does not set units for dimensions. To set the active units for dimensions, click Style on the Format menu and set the units for a dimension style. Active units control the format for dimensions when they are placed. For existing dimensions, you can click Properties on the Edit menu and set the units for dimensions that you have selected.
On the Units tab, set the options you want.