Each drawing window has vertical and horizontal rulers that show measurements at the scale of the drawing.
To change ruler measurement units, on the Page Layout tab, click Ruler button. Under Measurement Units, click the units you want.
To change the spacing of ruler subdivisions, press F6 key to open the Page Setup dialog, and then click Ruler & Grid. Under Subdivisions, click the spacing you want.
Note For some types of drawings, you may want to change the measurement units to pixels. However, a pixel isn't a unit of measurement. A pixel is just a dot on a screen and the size of the dot varies for different screens.
(Ctrl + Shift + R)
On the View menu, click Rulers.