Book review community site Goodreads has reached 20 million total users, the company announced today.

The service allows people to share their thoughts on books, or even offer full reviews of those titles, which is extremely useful to both publishers and bookstores — and a big reason Amazon purchased the site back in March.

Today’s announcement is interesting because it means Goodreads has essentially doubled its users since August 2012. Goodreads founder Otis Chandler also disclosed that the site has 25 million total reviews and has had users add more than 620 million books.

Chandler attributes the massive growth to a more well-rounded library of reviews across all genres and increased mobile activity from people looking up books inside physical stores before making a purchase. (I admit, I use the hell out of my smartphone before buying most books in a store, with Goodreads being the most likely service that pops up.) There’s also been a nice boost in international usage, Chandler told TechCrunch.

However, the real question is whether Goodreads has been able to boost book sales to Amazon — or at least divert those sales away from competitors.

Via TechCrunch