HOW MANY BOOKS

My 8 year old asked out of the blue, the way kids do, "Dad, how many books are there?"


After some discussion, it emerged that he was looking for a count of all the books ever published.


Using rough back of the envelope techniques I teach engineering freshmen, I conservatively estimated an upper-bound of about 500 million.


Then I looked it up online. Turns out Google did a count just a couple of years ago, and found that there were about 174 million known unique works.