Home » Tip of The Day » Changing Ruler UnitsChanging Ruler Units November 16, 2016. Posted in: Tip Of The Day. To change Ruler units, double click on the ruler to display the Units & Rulers preferences dialog box, or right mouse click on the ruler area to select a unit. « Previous Photoshop Tip: | Next Photoshop Tip: » Sign-up for the PTC Newsletter so that you'll never miss a tutorial!. Your Email Address: