As a quick followup, Britannica also claims that the 32 volume print encyclopedia has 44 million words.
I just picked a random article of 2,245 bytes, which was also 376 words. That implies just under 6 bytes per word. This statistic could be improved by checking more articles, but the article looks pretty normal to me, so I think it's basically a sensible ballpark figure for now.
150,000 articles averaging 2,126 bytes means 318,900,000 bytes total or just over 53 million words.
Considering *just* the 75,000 articles over 1500 bytes and assuming conservatively that these are all *only* 1500 bytes long (manifestly untrue), we are looking at 18,750,000 words for just those longer articles.
It seems clear to me that we are already "in the ballpark" of the size of Britannica. Quality is, of course, an entirely different question. I think we are often superior and often drastically inferior. I susppect that our coverage contains strange and conspicuous 'holes' if we went through it via a "top down" approach, i.e. take lists of major topics and see if we've covered them.
--Jimbo