Description: Your map is in the Layout window, now you would like to add a scale bar.
Methodology: 1) In your layout view highlight the data frame that includes the data layers to which you would like to add a scale bar. To select it click on it once.
Select your the data feature you want to display
Note: If the wrong data frame is selected then your scale will have incorrect measurements.
2) Then select Insert -> Scale Bar
Insert a scale bar
3) The Scale Bar Selector window will appear. Choose the style you would like to use for your scale bar.
Scale bar selector
4) You can further change the specifics of your scale bar by clicking the Properties button.
5) When you have made all your selections click Ok .
6) You scale bar will appear in the center of your map layout.
You can then resize it and drag to the desired location on your map layout.
7) You can further change the scale bar by double clicking on it and following the menu commands.