Demonstrators arrive in downtown Washington via Metro for the March for Our Lives on Saturday. (Toni L. Sandys/The Washington Post)

Metro said Sunday that ridership Saturday was 558,735 — about 2 ½ times more than a normal Saturday. No, it’s not a record . . . but there are few better ways to create controversy in Washington than by trying to estimate the size of a crowd that arrives to protest almost anything.

The National Park Service, which bears responsibility for the Mall, is loath to respond to the question — most often asked by reporters — “How big was the crowd?” Look no further than the dispute over President Trump’s inauguration to understand how thoroughly it hates estimating crowds.

That’s why Metro ridership numbers come in handy. They are facts. Someone goes through a fare gate; that creates a record. Is it a complete record? No, of course not. People also arrive to protest or celebrate via planes, (non-Metro) trains and automobiles. Many often come by charter bus from distant cities, as they did for Saturday’s March for Our Lives.

This does not save Metro ridership facts from controversy, however. When Metro tweeted that it recorded 558,735 trips on Saturday, someone quickly tweeted back: “Any chance to get this stat for an even bigger event like the March for Life?”

Let the bickering begin. It’s important for @DougColinade, who fired off that tweet, to remember that the antiabortion protest March for Life takes place on a weekday, and that it’s an annual event rather than a one-time protest such as the March for Our Lives or the 2017 Women’s March on Washington, which both occurred on weekends.

By Metro ridership alone, the 2009 inauguration of Barack Obama holds the ridership record with 1.1 million trips, and it fell on a weekday. The 2017 Women’s March — on a Saturday — ranked second, with 1,001,613 trips. By contrast, on the day of Trump’s inauguration, a weekday, the system recorded 570,557 trips.

“There’s always something going on” in the District on a weekend, Metro spokesman Ron Holzer said, “but we had about 230,000 riders last Saturday.”

There’s a list of the 10 busiest days for Metro ridership, and five of them were when the cherry trees were blooming and something else happened the same day — most often a Wizards, Nationals or Capitals game.

Holzer said he saw news reports that 800,000 people attended Saturday’s March for Our Lives.

“Our ridership did not reflect that,” Holzer said. “I think a lot of the people came on [charter] buses because they’re kids and can’t afford hotel rooms.”

As to @DougColinade’s question: Holzer didn’t have ridership numbers handy Sunday for this year’s March for Life protest of the Roe v. Wade Supreme Court decision.

He pointed out, however, that it fell on a weekday, when ridership numbers can be deceiving because they include daily commuters.