When I work in PI with the intent to print, I change my unit of measure to inches in my preferences (File > Preferences > General). I open a canvas the size of a full piece of paper at my desired resolution, which is normally 300. When I want to resize a photo or objects as I'm doing my layout, I go to Format > Image size and resize using inches as my unit of measure there as well. This makes it much easier to get photo prints in the sizes I want and to create paper craft projects.

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~ Ginger