How many people attended the Travis Scott concert inside Fortnite?

How to get close to this number

Cap it by concurrent players. The game had tens of millions of active players at the time, and a headline event pulls a large minority of them into the same session. Ten to fifteen million simultaneous is the ceiling for a game of that size, and this hit the top of it.

The comparison in the explanation is the one that reframes live music: total attendance across replays exceeded any physical tour in a single year. A venue is bounded by seats and a tour by nights; a virtual event is bounded only by servers, which removes the constraint that has defined live performance economics for the entire history of the form.

The timing matters — April 2020, when physical events were impossible everywhere. That is not a coincidence but it also is not the whole explanation, since the format has continued since. The record stands as the moment it became clear that a game client is a viable venue, and the audience numbers are ones no stadium can approach.