What Methods Are Used for Crowd Counting?
The most common method for estimating the number of people in a large crowd, known as Jacobs Method, is actually pretty straightforward. The technique is named after Herbert Jacobs, a professor of journalism at UC Berkeley who came up with it while trying to estimate the size of the Vietnam War protests outside his office window in the 1960s.
Jacobs noticed that the ground outside was gridded so he could carefully count how many protesters were in one square on the grid and then multiply by the number of squares. Thus crowds in spaces like the National Mall that are laid out in a natural grid-like pattern can be easier to tally.
If a rally space is not so conveniently gridded, knowing the total area, along with the density of the crowd, is also sufficient. The most tightly packed crowd, known officially as “mosh pit density,”
has one person per every 2.5 square feet. This is the sort of crowd where, if you were able to pick your feet up off the ground, you’d be so squished by those around you that you’d probably stay upright just fine. This density of people is considered a strict upper limit—any crowd counts that allot less space per person are not considered physically possible.
A more breathable crowd puts one person per ever 4.5 square feet which still places you elbow to elbow with your neighbors. A light crowd might have one person per every 10 square feet. Thus breaking up the landscape into higher vs lower crowd density chunks and then multiplying by their relative areas can give very estimates of crowd size usually within 10-20%.