Are picas getting you down?

Here's a way to convert units in a hurry! No more dredging around in that cumbersome Preferences submenu, just do what the pros do:

In any units dialog box, type the number of units and the unit of measurement, such as "9 in" for nine inches. If preferences are set to a unit other than inches, the software will do the conversion for you.

OR.....

Here's a handy Photoshop / Illustrator trick if you're constantly flipping between pixels and inches for web and print work: Rather than going into the program's preferences to change the unit of measurement, try this; first, make sure that the rulers are turned on (Ctrl+R in Windows; Cmd+R on the Mac); then try right-clicking (Windows [or Mac]) or Ctrl+clicking (Mac) on either the horizontal or vertical ruler within your document. In the pop-up menu that appears, you can switch the unit of measurement being used.

— Geoff Blake for Dynamic Graphics, graphics.com/learning