The Pew Research Center has published the results of its latest bi-annual survey into American reading habits. A survey conducted in early January 2018 showed that the number of Americans reading books has essentially remained unchanged since 2012:
About three-quarters (74%) of Americans have read a book in the past 12 months in any format, a figure that has remained largely unchanged since 2012, according to a Pew Research Center survey conducted in January. Print books remain the most popular format for reading, with 67% of Americans having read a print book in the past year.
And while shares of print and e-book readers are similar to those from a survey conducted in 2016, there has been a modest but statistically significant increase in the share of Americans who read audiobooks, from 14% to 18%.
The report from Pew says that "Americans read an average (mean) of 12 books per year, while the typical (median) American has read four books in the past 12 months".
I think it better to exclude the non-readers and non-answers, and focus instead on those who read. This raises the median to well over 7 books a year. (I am uncertain how to calculate the mean from the provided data, however.)