Google, during its ambitious crusade to digitise every book every written, has been keeping count of just how many books there are in the world and has come up with a total - 129,864,880.

You may be wondering how exactly Google arrived at this whopping number. Well wonder no longer because we at Pocket-lint are on hand to tell you (with a big slice of help from the official Google blog).

First of all it had to classify exactly what was meant by the term book. So it used a mixture of 150 different provider's meta-data including "libraries, WorldCat, national union catalogues and commercial providers".

From this it had a total of almost a billion. After further analysis it shaved this raw number down to around 600 million.

Within this 600 million, Google explains that there are still many duplicated entries as well as books that have been incorrectly labelled:

"When evaluating record similarity, not all attributes are created equal. For example, when two records contain the same ISBN this is a very strong (but not absolute) signal that they describe the same book, but if they contain different ISBNs, then they definitely describe different books. We trust OCLC and LCCN number similarity slightly less, both because of the inconsistencies noted above and because these numbers do not have checksums, so cataloguers have a tendency to mistype them".

After some more number crunching and some incredibly confusing algorithms, Google got the number down to around 210 million.

But then it had to exclude "non-books such as microforms (8 million), audio recordings (4.5 million), videos (2 million), maps (another 2 million), t-shirts with ISBNs (about one thousand), turkey probes (1, added to a library catalogue as an April Fools joke), and other items".

After this step the number stood at 146 million but is further reduced to the 129,864,880 total by excluding serials that are still duplicated in the Google system, such as different ways to describe volumes (such as shortening to vol. or V).

So we now know two things. Firstly, there are 129,864,880 books in the world. And secondly, some of the guys over at Google have got far too much time on their hands.