Comparison of the eight largest TNOs. Five of these TNOs are known to have moon(s). 2007 OR10, Orcus, and Quaoar are all estimated as about the same volume. Since Quaoar and Orcus have moons, it is known that Quaoar is much more massive than Orcus. The top 4 are official dwarf planets while the bottom 4 are dwarf planet candidates.
There may be an updated version of this graphic available at <a href="http://en.wikipedia.org/wiki/File:EightTNOs.png">Wikimedia Commons</a>.