If you go to the View menu in Photoshop and click on Print Size then you should see your image in the screen at it’s actual print size. At least that’s what should happen …
This would be a really useful feature if it actually worked, being able to see an image at the actual size you want to print it makes alot of things alot easier. For example judging the amount of sharpness used, or seeing the amount of visible detail in the shadows when soft proofing.
Unfortunately in Photoshop’s default state it will only work if your screen is running with a ppi (pixels per inch) of 72, which most don’t do anymore.
To fix this first work out your screens actual ppi then go to Photoshops Preferences->Units & Rulers and enter your ppi into the Screen Resolution input box.
To work out your ppi simply divide your screens horizontal resolution by the physical width of the screen. In my case that was 1920(pixels) / 20.5(inches) = 93.66ppi. Remember to select pixels/inch if you measured your screen in inches or pixels/cm if you used cm’s.