If I was sending out a single image to print rather than an array of photos on a page, I'd probably just use Export as others have said, above; however, in my LR 5.6, if I change the output type to JPEG, I see an option to customize the file dimensions of that JPG output. I do need to adjust the cell size if the virtual page has different dimensions than the original physical page of the selected printer. I have an HP LaserJet set as my output printer prior to switching to JPG. I see this Customize File Dimensions option in all three Layout Styles: Single Image / Contact Sheet, Picture Package, Custom Package.
