How do I set resolutions to get good results in print?

[Hai-Etlik]

Incidentally, the printed size of the image will still likely be different because Gimp doesn't know how large your screen is.

Yes it does actually, at least if the OS/Windowing system knows and reports it accurately.

[Midgardsormr]

Yes it does actually, at least if the OS/Windowing system knows and reports it accurately.

Truly? I did not know that. In any case, though, I can't speak for every system (and not for Gimp at all, since I use PS), but I have seen no indication that my OS has ever known the physical dimensions of my screen. I currently have a very new full HD monitor connected via DVI, and although Windows has a lot of information about it, physical size does not seem to be one of those. Further, Photoshop has no apparent switch to enable it to take such data. You can, however, set the default screen resolution manually through Edit > Preferences > Units and Rulers.

[Hai-Etlik]

Truly? I did not know that. In any case, though, I can't speak for every system (and not for Gimp at all, since I use PS), but I have seen no indication that my OS has ever known the physical dimensions of my screen. I currently have a very new full HD monitor connected via DVI, and although Windows has a lot of information about it, physical size does not seem to be one of those. Further, Photoshop has no apparent switch to enable it to take such data. You can, however, set the default screen resolution manually through Edit > Preferences > Units and Rulers.

Well I don't know about Windows, but X.org on Ubuntu has no problem with this. I can use xdpyinfo to bring up all the information about my display and dimensions and resolution are right there.

screen #0:
  dimensions:    1280x1024 pixels (339x271 millimeters)
  resolution:    96x96 dots per inch

It's a rather old monitor, it doesn't even have a DVI input.