First, go to your System Preference and click the Displays icon.The key to seeing things actual size in Photoshop is to make Photoshop and your screen the same resolution. The problem is that modern computers/screens are much higher resolution than 72 dpi. Create an 8.5 x 11 inch document in Photoshop, set the view to 100% and hold up a Letter size piece of paper and you’ll notice the difference. Unfortunately that hasn’t been the case in many years. That’s because when Adobe coded 100% view, it was based on all screens being 72 dpi. It’s almost always larger, depending on your Mac. Ever notice that when you view a Photoshop file at 100%, it’s not actually 100%.