For those who like numbers that’s 12,043,858 books (as of today).
For example, here are books with Lexile measures from 580L-720L. The sliders that allow you to find a range of levels are very useful. Kudos to Tim S. for making them available.
If you’re a LibraryThing member, you can quickly access lexile measures for your library by using the following URL: http://www.librarything.com/memberlexile/MEMBERNAME
Lexiles come into your library at three levels. First, you can manually edit them. If you have not, it looks to the ISBN level, the level MetaMetrics correlates to. If that comes up empty it looks to the work level, which is extrapolated from other ISBNs. On occasion this fails, generally because a simplified edition of a book has been included within the larger work. We are working to improve the work-level matching.
The remainder of the blog post has some background (including a mention of school librarians and teachers) along with a links to the Lexile map and more info. Btw, these links are also located on every page where measurements are found plus a list of Lexile Codes.