There are a bunch of estimates out there, but the best guess is that starlink can currently serve around 300 terminals per cell. Each cell is 146 miles, which

There are a bunch of estimates out there, but the best guess is that starlink can currently serve around 300 terminals per cell. Each cell is 146 miles, which is around 2 terminals per square mile. People may be clustered a bit, giving the illusion of starlink being able to support a higher density than this. Starlink isn't as scalable as people want to imagine due to the RF bandwidth SpaceX has as well as power requirements. This is part of why SpaceX made such a big deal over the 12GHz band that Dish wants to use. The next version of satellites may be able to support additional bands which will help, but starlink's still going to be fairly limited in terms of number of people it can support.