The ruler in Word 2016 displays horizontally across the top of your workspace, and can be used to align text, graphics, tables, and other elements in your document.
To display the ruler if you can't already see it, go to the View tab and make sure that Ruler is checked (in the Show group).
Similarly, you can hide the ruler in order to make more room for your document by unchecking the checkbox.
Even if you have Ruler checked, you will not see it in Read Mode, or Outline View. However, it will be displayed in all the other views.
But what is the ruler’s unit of measure, I hear you ask? Is it centimetres or is it inches? To find out, and also to change the ruler’s UOM, click File > Options > Advanced, and scroll to the Display settings. The Show measurements in units of selector displays the units currently being used by the ruler (and everywhere else in the document).
You can change the UOM to any one of:
Make your selection and then click OK.