If images or PDFs aren’t the correct size in Preview on Mac
By default, in Preview, PDFs display at the same size on screens and in printouts, regardless of the display resolution, and images display showing 1 point on screen for 1 point in the image. For example, a PDF that measures 8.5x11 inches always appears on screen as 8.5x11 inches, and an image displays as one size on screen and another size when printed. This variation may lead you to wonder if a PDF or image file is the wrong size.
You can change the default 100% scale settings to your preference.
In the Preview app on your Mac, choose Preview > Preferences.
To choose how to display documents, click PDF or Images, then choose an option next to “Define 100% scale as”.
To display a PDF or image at the same dimensions regardless of the screen’s resolution, select “Size on screen equals size on printout”.
To display a PDF or image at different dimensions depending on the screen’s resolution, select “1 point equals 1 screen pixel”.