I was just reading this Bloomberg story on Google's investments in the VR space, which included this intriguing "Virtual Insanity" chart:

So Bloomberg Intelligence and Gartner forecast VR equipment sales (not counting smartphone-based VR equipment*) to hit $21 billion by 2020. I really wish analysts would break down estimates like this more clearly, because the average reader just goes "Whoa, that's a lot of money", without really knowing what it means. So let me try and clarify:

According to this Bloomberg Intelligence/Gartner forecast, by 2020, people will buy less than 42 million units of Vive, Oculus, Playstation VR, and other high-end VR devices.

Divide $21 billion by an average device price of $500 (Oculus and Vive are currently more, but assume their prices go down every year), and 42 million is what you get. That might seem like a lot, but really, that just makes premium VR devices a subset of the overall videogame console/PC gamer market: