Miguel Medina / AFP - Getty Images
Anywhere from 100,000 to 2 million people gathered in Cairo's Tahrir Square, depending on whom you believe.
Update 1:10 p.m. ET: Al-Jazeera has now cut its estimate in half. Earlier: "up to two million." Now: "more than a million."
Wired, meanwhile, offers a way to guesstimate a big crowd.
Estimating crowds is a notoriously inexact science, so much so that the National Park Service stopped doing it for protests in Washington many years ago. That leaves it up to news organizations to make their best guesses.
So it's no surprise that estimates of the crowd that gathered today in Cairo's Tahrir Square are very imprecise and wide-ranging:
• Washington Post: "Tens of thousands, perhaps hundreds of thousands."
• New York Times: "Hundreds of thousands."
• Wall Street Journal: "Hundreds of thousands."
• Associated Press: "more than a quarter of a million people."
• Reuters: "At least one million people."
• Al-Jazeera: "Up to two million."
• BBC: "More than 100,000."
• Guardian (U.K.): "An estimated one million people."
• Telegraph (U.K.): "Estimated crowd of more than 1 million."
In January 2009, shortly before Barack Obama's inauguration as president, Steve Doig, a journalism professor at Arizona State University specializing in data analysis, wrote this explanation of why crowd-counting is a mug's game.