It's already up to 5.1 million. I might need to up my estimates by a million or so. 
It accounts for every platform combined (console, PC, mobile and cloud).
Edit: I should mention it only accounts for people in servers. So the true number of people who are actually in client is higher. How much higher? I really have no idea, but if you extrapolate based on other games such as Rocket League and Mordhau, you could probably add another 20-30%.
What site has the Fortnite concurrent player count?
It accounts for every platform combined (console, PC, mobile and cloud).
Edit: I should mention it only accounts for people in servers. So the true number of people who are actually in client is higher. How much higher? I really have no idea, but if you extrapolate based on other games such as Rocket League and Mordhau, you could probably add another 20-30%.