March on Washington: How Big Was the Crowd?

"How big is it?" is certainly one of the world's most dreaded questions.

In fact, after the Million Man March in 1995, Congress restricted the National Park Service from even making estimates -- a restriction that was maintained for 14 years and then quietly rescinded this January for the Obama inauguration.

I'm talking about crowds, of course. I can't take you people anywhere.

There have been a lot of estimates, from the "official" one of 60 to 70 thousand, up to the rumored 2 million. Let's see if we can make a plausible estimate with some rigor and some idea of possible error.

Yesterday, I made a back of the envelope calculation that Stephen Green picked up at Vodkapundit, simply to see if the high estimates were at all plausible. A number I picked up by Google searching told me that a pretty good crowd is about 18 people in 10 square meters -- that's about half as crowded as a crowded elevator (approximately one person per six square feet).

Wikipedia told me that the National Mall covers about 125 hectares, or about 1.25 million square meters, and simple multiplication then tells us that if the whole mall was that crowded, that would be as many as 2.3 million people. Which is one hell of a crowd. Call that an upper bound -- anyone who says it was more than 2.3 million is almost certainly wrong.

Just for comparison, we've got the Obama inauguration, which was originally estimated at 2 million and then revised down to about 850,000. Popular Science got GeoEye to take a satellite photo.

Now, via Green, we have a number reported by Barbara Espinosa from the "people meter" on Pennsylvania Ave -- a total of 1.5 million people passed by during the march. Now, that's some kind of direct count, but we don't know what kind -- if anyone has any information on this "people meter" I'd love to see it -- so let's save that as an estimate and see what else we get.

The National Park Service actually has a methodology for crowd estimation; they just were forbidden by Congress from using it after the Million Man March came out to be less than half a million. That restriction mysteriously disappeared for the Obama inauguration, and USA Today published a useful article on it.

Turns out the Park Service thinks a crowd is about one person per five square feet, or a little more dense than I used, but they clearly use a different area for the Mall than I got from Wikipedia -- they say a full Mall is about 1.5 million. So all we need is an overhead photo, and we should be able to compare easily, right?

The only problem is that I can't find one. No one paid to have GeoEye take one (next time, dammit) and no one has published one that I can find.


So let's take another approach. We've got Barbara Espinosa's 1.5 million count. Is that plausible?

Here we have other comparable data, in the various pictures from Pennsylvania Avenue. There is a time lapse from the traffic camera at 14th Street, roughly where E would cross 14th NW if only E actually crossed 14th. It's overlooking the Freedom Park, and looking down Pennsylvania Avenue to the Capitol. The White House is basically behind us from this point of view.

What that shows us is Pennsylvania Avenue full of people walking past for at least three hours. (This matches some other independent accounts, like this at the New York Times.) So more back of the envelope: it's 1.1 miles from Freedom Park to the Capitol, and Pennsylvania is six lanes plus a middle turn lane and some sidewalks -- call it 100 feet wide. That's about 600,000 square feet, so if it were a crowd standing still, that is at least 100,000 people. We've got a picture of that, so that's got to be a lower bound. We've also got a variety of pictures of at least the part of the Mall from 3rd to Capitol Circle and it's pretty full -- the Park Service method tells us that's around 250,000 right there.