I am using InDesign CC 2015 with an Epson stylus photo 3000 printer. I have a project that measures 8.5" (wide) x 5.5" (tall). It is setup as a letter document with a horizontal orientation. When I print it out to proof it, it measures 8.75" x 5.75". If I copy and paste the work onto a new document, but change the document size from letter (horizontal) to tabloid (vertical) size sheet, the size is printed correctly at 8.5" x 5.5". Why? If I then copy and paste that exact same project back into a new letter document, it will again print it out larger at 8.75" x 5.75". I have checked the printer output dialog box and it is printing at 100% in all cases. Why won't it work on a letter size document?
It's possible to have custom page sizes that are a different size than the document. Try selecting the page with the Page tool and check it's size in the Transform panel. Also when you print check marks and bleeds-- you might be printing the bleeds.