This figure is in addition to the impressive $110 million worth of revenue generated by the game as of June 2.
Congrats everyone! We've officially reached 19 million players for Rocket League! We are humbled by your passion. Thank you!— Rocket League (@RocketLeague) July 18, 2016
These numbers don't even include downloads from when the game was free as part of PlayStation Plus, making it all the more impressive.
Rocket League was released on PC and PlayStation 4 in July 2015 and Xbox One in February 2016.