How Many People Will Attend Trump's Inauguration? Why to Take Turnout Estimates With a Grain of Salt

President-elect Donald Trump said his inauguration will have "unbelievable, perhaps record-setting turnout," but President Barack Obama's crowd estimate in 2009 may be hard to beat.

And experts say every crowd estimate should be taken with a grain of salt.

Obama drew an estimated 1.8 million people to the National Mall eight years ago, according to federal and local agencies. Planners say they are expecting no more than 900,000 people to attend Trump's ceremonies Jan. 20.

The D.C. Department of Homeland Security and Emergency Management is planning for 800,000 to 900,000 people to attend the swearing-in ceremony and inaugural parade.

The U.S. Armed Forces Joint Task Force-National Capital Region (JTF-NCR), which provides support for the ceremonies, is expecting 800,000 people.

The Joint Congressional Committee on Inaugural Activities (JCCIC), which plans and executes all ceremonies, is expecting 700,000 to 750,000 people.

• [Quote] Crowd Size Estimates

And Washington's destination marketing group, Destination D.C., is expecting 1 million people, when protesters are included in the count.

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Trump's Presidential Inaugural Committee did not respond to inquiries about how many people they expect.

Estimates for inaugural crowds vary, but Obama is widely believed to have set the record for most well-attended inauguration. Former President Lyndon B. Johnson held the previous record, drawing an estimated 1.2 million people in 1965.

Here are the widely cited estimates for recent inaugurations:

• President Bill Clinton, 1993: 800,000 people
• President Bill Clinton, 1997: 250,000 people
• President George W. Bush, 2001: 300,000 people
• President George W. Bush, 2005: 400,000 people
• President Barack Obama, 2009: 1.8 million people
• President Barack Obama, 2013: 1 million people

But experts say crowd counts always should be viewed with caution.

"Anybody who is just saying there were a million people there without saying what method they used, that's just public relations being offered," said Arizona State University journalism professor Steve Doig, who specializes in estimating crowd sizes.

"Take any estimate with a grain of salt," he continued. "What you need to do is look carefully at how the estimate was done and how transparent the group who did it is about their methods."

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How Do You Count a Crowd?

Crowd size estimates are reached using aerial images taken from satellites, helicopters and balloons, plus basic math. Three pieces of information are needed: the total area of the space, the proportion of the area that is occupied and the density of the crowd.

Analysts' estimates of crowd density tend to be where they disagree. 

In a loose crowd, people stand at about arm's length of each other, with about 10 square feet per person. In a dense crowd, each person has about 4.5 square feet. And in a dangerous, shoulder-to-shoulder crowd, each person has just 2.5 square feet to him or herself.

These figures and this crowd-estimating method are attributed to University of California, Berkeley professor Herbert Jacobs, who calculated the size of anti-Vietnam War protests at the university. From his office in a tower, he counted how many protesters fit in each square of a plaza marked with grid lines and then multiplied.

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Doig calculated before Obama's 2009 inauguration that as many as 2 million people could fit between the Capitol Building and the Lincoln Memorial if people were tightly packed from the Capitol to 17th Street NW and more loosely assembled further west.

After the inauguration, he estimated based on analyzing satellite images, TV footage and Flickr photos that Obama drew just 800,000 people.

The 1.8 million figure is what federal agencies, D.C. agencies and then-Mayor Adrian Fenty's office calculated, The Washington Post reported at the time. The National Park Service said the agency believed Obama had the largest crowd ever and did not contest the 1.8 million estimate.

The defense analysis firm IHS Jane's estimated 1.271 million to 1.651 million, McClatchy reported. The Associated Press estimated more than 1 million and McClatchy about 2 million.

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To attempt an accurate estimate, analysts must take into account differences in crowd density in different places of the Mall. For example, far from the Capitol, crowds are often clustered in front of Jumbotrons but more sparse elsewhere.

And photos can be deceptive. Images that are taken from low angles and show large areas make crowds seem more dense than they are.

"All you can see is what looks like a sea of people," Doig said. "It looks more solid than it actually is."

Who Will Estimate Trump's Inaugural Turnout?

So, who will count the crowd this time? Private companies may take and analyze aerial images. 

But as for an official count, it's not immediately clear.

Congress ordered the National Park Service to stop issuing crowd estimates after the agency gauged the crowd at the Million Man March in 1995 at about 400,000 people. That estimate drew the threat of a lawsuit from leader Louis Farrakhan, who called the figure defamatory and threatened to sue. (Using aerial images and basic math, a team at Boston University determined that between about 670,000 and 1,005,000 people attended.)

The Park Service will not release a crowd estimate after Trump's inauguration, a spokesman said.

The JCCIC and JTF-NCR inaugural planning groups both said they also will not issue estimates of Trump's crowd after the festivities.

Trump's inaugural committee did not respond to inquiries about whether they plan to issue an estimate.

In a tweet sent last month, the president-elect urged supporters to attend. 

The Boston University team that calculated the size of the Million Man March said they do not have a week to spare to do the count this year.

And as Doig, the Arizona State University crowd estimator, considered whether to measure the size of the crowd Trump draws, he considered responses he received to estimates he made in 2010.

He got nasty calls and emails after he calculated the size of the crowds at Glenn Beck's "Restoring Honor" rally and Jon Stewart's "Rally to Restore Sanity and/or Fear."

"Why are you lying?" some of the messages said.

This time, he decided he'll stay out of it.