This is a visualization of what Wikipedia would look like printed out in Encyclopædia Britannica volumes. 1,908 of them to be exact. Good luck selling those door-to-door, Willy Loman! Dickbag. "Huh?" You bought your mistress new stockings while your poor wife was mending old ones!
This shows 2,537 million words across 4.3 million articles (for August 2013), implying an average of 590 words per article.
Same source shows 19.83 GB (=20,498,960 B) across 2,537 million words, implying 8.08B/word. ASCII uses 1B/character which in turn implies 8.36 characters/word. However, this includes wikimarkup, and 5 char/word plus one for space is standard, so 6 characters/word will be assumed.
There are currently 4,309,964 articles, which means 2,542,878,760 words, which means 15,257,272,560 characters.
One volume: 25cm high, 5cm thick. 500 leaves, 2 pagefaces per leaf, two columns per pageface, 80 rows/column, 50 characters per row. So one volume = 8,000,000 characters, or 1,333,333 words, or 2,259.9 articles.
Thus, the text of the English Wikipedia is currently equivalent to 1,907.2 volumes of the Encyclopædia Britannica.
Sanity check: Encyclopædia Britannica has 44 million words across 32 volumes, or 1,375,000 words per volume. This would imply 1,849 volumes for WP.
I didn't bother crunching any of those numbers because I am a terrible number cruncher but I do chew with my mouth open which most people can't stand but it doesn't bother me. I slurp soup too which I heard is actually complimentary in Japan but will get you smacked in the back of the head with a wooden spoon in my aunt's kitchen. "It sounds like you're trying to suck off a giant" she tells me.
Thanks to Dunc, who's determined to read every word.