Astronomer and artist Rhys Taylor has made such comparisons easier and much more fun with his new infographics ("which is what I gather is now the cool term for 'posters,'" he writes) comparing the sizes of different galaxies.

The graphics are well worth exploring. They show the diversity in sizes and shapes of galaxies and offer interesting facts, like that some galaxies emit jets, powered by black holes in their centers. See them in their full glory at Taylor's website.