In Photoshop, the shortcut is Alt-Ctrl-I (or go to Image, then click on Image Size) and you should see this screen:
As long as Constrain Proportions is checked, you should just have to change either the width or the height to the amount of inches you want and the other value will automatically change to remain a square. Whenever I use QPs, I always resize them to 8 x 8 for printing purposes, but I always make them 12 x 12 just in case.
Hope this helps! :)