preview image highlighting ruler

Adobe Photoshop’s rulers are really useful when you’re cropping, combining, or otherwise editing your images. Depending on what you’re doing, you might want them to display pixels, percentages, or even inches. Here’s how to change their units.

How to Show Rulers

photoshop rulers highlighted
Photoshop’s rulers show outside of the image.

If you don’t see the rulers on the edge of your document, go to View > Rulers, or use the keyboard shortcut Control+R (Command+R on a Mac).

show rulers menu option

You can hide the rulers if you don’t need them. Use the same commands.

How to Change the Ruler Units

ruler pixels inches
These rulers are showing pixels and inches.

Adobe Photoshop supports seven unit types:

  • Pixels
  • Inches
  • Centimeters
  • Millimeters
  • Points
  • Picas (1 pica = 12 points)
  • Percent

The quickest way to change between them is to right-click on a ruler and select the option you want from the drop-down menu.

unit change dropdown

You can also change the unit through Photoshop’s preferences pane. Go to Edit > Preferences > Units & Rulers. (On a Mac, go to Photoshop > Preferences > Units & Rulers.)

Under “Units,” click the “Rulers” dropdown, then select the units you want to use.

Note: When you change the ruler units in one document, it changes them in all your open Photoshop documents.

changing units in preferences pane

Can You Change the Default Ruler Units?

Unfortunately, there’s no way to change the default ruler units or set them to match your images’ measurements. Photoshop remembers the last unit you used.

Can You Set Different Ruler Units for Different Documents or Presets?

Again, unfortunately not—you can’t set different ruler units for different documents in the application. The ruler unit is a global setting. If you change it in one Photoshop document, it’s changed in all Photoshop documents.

(Yes, this is super annoying if you’re editing images and laying out print designs at the same time.)

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Harry Guinness is a photography expert and writer with nearly a decade of experience. His work has been published in newspapers like The New York Times and on a variety of other websites, from Lifehacker to Popular Science and Medium's OneZero.
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