Here is another list of DSOs with sizes as well as images.
http://www.deepskywatch.com/deepsky-guide.html
Most DSOs are small. NGC 5139 (Omega Centauri) is just over full moon in apparent size and a good example to compare others. It is also visible unaided. Most galaxies are tiny in apparent diameter. Note also when looking at a galaxy you mainly see the core as the outer portion is faint.