The Hubble Space Telescope Deep Field survey found enough galaxies in the few arcminute field it studied to be equal to about 2 - 3 million galaxies per square degree of the sky. With 42,000 or so square degrees in the sky, this means that there are AT LEAST 80 - 120 billion galaxies in the visible universe. There are probably much more than this by perhaps a factor of 10, because for every bright massive galaxy you see, there are many more faint, dwarf galaxies like the Magellanic Clouds that orbit the Milky Way, and which would be impossible to see at great distances.