There are many ways to change rulers in Adobe Photoshop. You can use the rulers tool, the eyedropper tool, or the selection tool. The selection tool is especially helpful when you want to change the size of a ruler. To change a ruler unit in Adobe Photoshop, follow these steps:

  1. Choose the ruler tool from the Tools palette.
  2. Drag one of the ruler units off of your canvas and onto another location on your document. For example, if you want to change the size of a ruler unit, drag it off of your canvas and onto a smaller location on your document so that it covers all of your canvas area.
  3. Release the mouse button and select another ruler unit from the Tools palette to replace the first one that was removed from your canvas.

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

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).

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

How to Change the Ruler Units

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.

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.

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.)