The BBC’s fact-checking unit, BBC Verify, has concluded that about 660,000 people could have attended Lady Gaga’s free 3 May concert on Rio de Janeiro’s Copacabana beach—less than one-third of the 2.1 million claimed by the city government and entered in Guinness World Records as the largest free show by a female artist. Using aerial images, maps and crowd-density guidelines that cap safe occupancy at 4.7 people per square metre, the broadcaster calculated that the audience occupied roughly 140,000 square metres, equivalent to 20 football pitches. Even doubling that density and counting spectators on balconies would not reach the official figure, the analysis said. Experts told the BBC that the full 4-kilometre beach, around 610,000 square metres, could hold two million people, but the event filled only a portion of the shoreline. Rio tourism agency Riotur and Mayor Eduardo Paes rejected the revision, insisting their 2.1 million tally is accurate and criticising the BBC’s methodology. City officials have not released their own calculation model. The dispute revives long-standing questions about how authorities measure crowds at large open-air events in Brazil. Guinness World Records said it is monitoring the discussion but has not amended the entry.