March on Washington: How Big Was the Crowd?
Our attempt to calculate the true size of the 9/12 march.
September 14, 2009 - by Charlie Martin:

Conclusion: probably well more than 850,000 in the crowd.

An Impression Of The Protest:

the evidence indicates this demonstration was at minimum still over two hundred thousand, and most likely three hundred thousand-plus, possibly as large as five hundred thousand. “Hundreds of thousands” is the non-misleading and defensible description.