If you use Goodreads to track what you read, you get some stats per year, like number of books read, number of pages read.

Mine: https://www.goodreads.com/review/stats/63629672-henrik-warne

I find it very useful, and especially by combining the two.

For example, in 2015 I've read more than double of the amount of books I've read this year, but comparing by the number of pages, the difference is just a few dozen pages.

While the amount I've read remained steady, I'm clearly able to retain longer focus necessary to read longer titles, which is something I wouldn't easily spot in such a short timeframe otherwise.

Also there are apps to block social media while reading: Offtime app works great.