You can’t show rulers in Word Online unfortunately. But if you have the Word desktop application, click Open in Word to open the document and see rulers.
To learn more, see Show or hide rulers in Word or Show or hide the rulers in Word 2016 for Mac. If you don’t have the Word desktop application, you can try or buy it in the latest version of Office now.
Tip: Got a suggestion for this feature?
Vote for an idea, or share a new one in our suggestion box at word.uservoice.com.