All you boys have to do is look at the pics.
There's no magic to USA Today's methodology; they took the actual area and estimated at a person per 2.5 square feet. That's simple math.
The north glen alone is about half the size of the area estimated to hold 946,000. So, be conservative, round it down, say 400,000.
In the pic, it's filled, but not very densely, so say 1/4 of the density contemplated. That's 100,000 people right there.
The mall area, too, is almost that size; also being conservative, if it were all solid ground, it too would hold about 400,000. The reflecting pool takes up about 75% of the space, but of the people there, it IS densely packed, so it's a pretty fair estimation that it, too, is about 100,000.
That doesn't include the people around the memorial, around the middle pool, in the pathways, and obscured by the trees.
So, looks like at least 200,000 to me, through simple, conservative calculations.
And I really don't even care how many are actually there; I'm just fascinated with the need of some people to diminish it as much as possible and not admit it could possibly have been more than the lowest estimate one could find.