It and the File - Print Preview do show the relative scaled image size on the paper, if paper size is known and set. Print Preview has a ruler option marked in inches, but it's a little coarse. However, if they show inches, they no longer show pixels, also awkward. Puzzling why showing both should be difficult, not showing printed image dimensions in inches is a surprising weakness in such a strong program. This makes preparing images to be printed elsewhere, say for word processors or newsletters, be especially inconvenient.
File formats vary too.
TIF and JPG image files store this scaled resolution number for printing. The image file knows the size it should print. However GIF files do NOT store the scaling resolution number in the file. Nor do Kodak Photo CDs either. But programs must have a number to show for print scaling, and therefore must provide a default number for GIF files.