A reliable crowd estimate of people who came to the pope's public Mass here Sunday has been elusive, but a new number from the Archdiocese of Philadelphia gives a hint at the size of the throng.

The number is 260,000 - Communion wafers.

That many consecrated Communion wafers were consumed during the Mass on the Benjamin Franklin Parkway, said Stephanie Brophy, spokeswoman for the archdiocese. That's out of 300,000 wafers prepared, Brophy said.

She cautioned that the figures "should not be used for a crowd estimate indicator," saying city officials "would be your source for this number but they have not yet released the crowd estimate."

Indeed, the mayor's office and the Secret Service, which oversaw security planning for the weekend, have thus far declined requests for a crowd estimate.

Add the wafer totals, then, to the various clues to the crowd's size. One expert has estimated that 142,000 people filled spaces between the Philadelphia Museum of Art and 20th Street, based on an image that did not include several blocks of crowds. Ridership counts from SEPTA and PATCO showed 387,000 people entered Center City on Saturday and Sunday by subway or regional rail; Sunday travelers accounted for slightly more than half that total.

Though the wafers distributed at the Mass do not offer an exact count of people on the Parkway on Sunday, one expert said some conclusions can be drawn.

"At least half the crowd would have been Catholic, I would think," said Joel Best, a sociologist at the University of Delaware.

At Mass, 550 priests and 250 deacons fanned out to give Communion. Aides held yellow-and-white umbrellas to signal their locations. From the pope's altar near the Art Museum steps to as far east as 17th Street, crowds surged forward to receive the sacrament. A woman near 21st Street shouted to a priest, "Father! My sister is pregnant!"

The priest heard and gave the pregnant woman a wafer, but many others who extended their arms to receive the host left empty-handed.

Unused wafers were given to area parishes for use this week, archdiocese spokesman Ken Gavin said.

While officials aren't giving an attendance estimate, the means may exist to determine one key number. Among metal detectors used at papal events were some with the logo CEIA, an Italian company whose website indicates some models are equipped with an automatic people-counter.

Asked if that feature was used during the papal events, the Secret Service declined to answer.

Asked if other sources of information might be used to gauge crowd size, mayoral spokesman Mark McDonald said Friday in an email that he was not immediately able to reach city officials who could give specifics.

Counting crowds is a challenging task, experts said, and sometimes a controversial one. "I think that we use it as a benchmark to how popular a cause is, how many people are concerned," Best said.

Accurate counts are difficult in the absence of a confined, ticketed space such as a stadium.

Another expert in crowd counting, Clark McPhail of the University of Illinois, said the amount of space that a million people would fill is hard for the average person to visualize.

People often estimate an event drew a million people, McPhail said, because "it just rolls off the tongue so easily."

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Inquirer staff writer Laura McCrystal contributed to this article.