DC cops have a system, They look at the total area filled, then give each person standing 10 square feet (I think) to allow for non crowding, aisles, etc.
They give sitting people 20 sq feet I think. Assume at 700 feet by 300 feet, that's 210,000 sq ft; some standing, some sitting, minus the stage, minus those big open areas outside the circle, It's about 10K people +/-.
All in all, a big no show.