In Word 2013, you can select one of several units of measurement for the ruler. You may be working on a document for someone who measures their margins, tabs, etc. in a different set of units than you usually use. It’s easy to change.

Click the File tab.

Click Options in the menu list on the left.

The Word Options dialog box displays. Click Advanced in the menu list on the left side of the dialog box.

Scroll down to the Display section. Select an option from the Show measurements in units of drop-down list.

via How-To Geek http://www.howtogeek.com/169302/how-to-change-the-ruler-measurement-unit-in-word-2013/