Philadelphia celebrated its first Super Bowl parade Thursday honoring the Eagles' historic win against the New England Patriots, bringing throngs of fans from across the region into the city to catch the big event.

But just how many fans?

City officials had expected the "largest parade crowd in the city's history," suggesting that preparations should be made to accommodate more than two million people.

The Inquirer and Daily News commissioned crowd safety experts from Manchester Metropolitan University in England to give a scientific estimate. They said close to 700,000 people attended the parade, based on bird's-eye-view photos of crowds on Broad Street, around City Hall and along the Benjamin Franklin Parkway, along with calculating the available space for fans.

But fans were unsatisfied with their estimate. Very unsatisfied, actually, to judge from the angry comments on the story. A sample: "These Brits and their metric system. C– like this is why we started throwing their tea in the river. Go Birds."

And this: "Even the crowd counters underestimated us. Underdogs forever!"

Social media was similarly aflame. "Here's my estimate, 3.2 million," tweeted sports talk radio host Angelo Cataldi. His evidence: "I had a big advantage: I was there!"

Told of the furor on Friday, G. Keith Still, a professor of crowd science at Manchester, kept calm, carried on, stuck to his team's initial calculations, and provided a further explanation that resembled an SAT question:

Consider that if two or three people stand in each square meter of space (about the size of a card table), you'd need a million square meters (that's a square kilometer, or just over a third of a square mile) of completely clear land to hold two million to three million people. And there just isn't that much space along the route, he explained in an email Friday.

"It's the same whenever there is a 'huge' crowd claim, and why this is such an important topic to get right," he wrote.

Eagles officials did not return calls for comment.

Social media wasn't buying the English math.

Keep in mind, Philadelphia's population is about 1.6 million, while the greater metropolitan area is about 6 million. If there really were 3 million at the parade, that would be about half the region's population.

Getting a reasonable estimate starts with simple geometry, said Rich Di Dio, a professor of math and physics at La Salle University and a long-time Eagles fan who spent six hours at 22nd Street and the Parkway on Thursday.

"I thought for sure it was about 2 million," Di Dio said about the crowds.

But, being a scientist, he knew there was no way to actually count the people. He could, however, calculate the maximum number of people who could fit in the space along the route.

That exercise got him to reconsider his initial big number.

Di Dio used Google maps, and drew a trapezoid from City Hall to the Philadelphia Museum of Art to determine the area inside the figure. Figuring that each person took up 4.5 square feet, he concluded that 1.3 million people would fit in the space. Along the nearly four-mile route up Broad Street, he calculated that if there were 10 rows of people on each side standing shoulder-to-shoulder, that would yield 52,800 people per mile. Grand total: 1.5 million people.

But: Small problem. Everything in that trapezoid — buildings, trees, fountains, even the Parkway itself — would have to be removed to make room for all those people. And of course, removing the street would mean the parade couldn't come through.

Oh — and all those people could never, ever move to another spot along the parade route.

So, he said, forget 1.5 million. And really forget 2 million. "There is no way you could have 2 million along the parade route unless you had people stacked on top of each other," Di Dio said.

Perhaps wisely, however, the professor declined to name a number he thought more likely, or even to say what he thought of the 700,000 estimate.

Broad Street was jammed for the Phillies championship parade in 2008.
File Photo
Broad Street was jammed for the Phillies championship parade in 2008.
Eagles mascot Swoop leads the team buses up South Broad Street as the Super Bowl victory parade nears City Hall.
TOM GRALISH / Staff Photographer
Eagles mascot Swoop leads the team buses up South Broad Street as the Super Bowl victory parade nears City Hall.

Many expected a turnout similar to the Phillies' 2008 World Series parade, where numbers between 1 million to 2 million were rumored as crowd estimates. But no real crowd count or mathematically informed estimate was ever made there.

Mike Dunn, a spokesman for the mayor's office, said that the city would not be giving its own estimate of Thursday's crowd because "it would be too much of a guess."

"Clearly, we had hundreds of thousands, and the most important thing is that the overwhelming majority of people had a great time seeing and honoring the team," he said.

But during a news conference regarding the Super Bowl held Friday, city officials said the attendance was likely more than 700,000.

"I think we had more people than the Trump inauguration," Mayor Kenney cracked.