By convention, a skyscraper is a building that is used primarily for human habitation with the greatest majority of its height divided into occupiable floors. Freestanding structures used primarily for broadcasting or sightseeing are classified as towers. The height of a building is measured from the sidewalk level of the main entrance to the structural top of the building. This includes spires but does not include television antennas, radio antennas, or flagpoles. By this definition the tallest building is the Burj Khalifa, Dubai, United Arab Emirates, which was topped off in 2009 at 2,717 ft (828 m) and 160 stories; it is also tallest structure in the world. Taipei 101, Taipei, Taiwan, is the second tallest at 1,671 ft (509 m) and 101 stories in 2003. The twin Petronas Towers (opened 1997) in Kuala Lumpur, Malaysia, are the third tallest; 88 stories high and topped by twin spires, they stand 1,483 ft (456 m) tall. The Willis Tower (opened 1974, formerly the Sears Tower) in Chicago is the tallest building in the United States; its 110 stories rise 1,454 ft (443 m) with an additional 253 ft (77 m) for the television antenna on top.
Among the highest New York City skyscrapers are the Empire State Building, with 102 stories, 1,250 ft (381 m) high; the Chrysler Building, with 77 stories, 1,048 ft (319 m) high; 60 Wall Tower, with 67 stories, 950 ft (290 m) high; and the GE (formerly RCA) Building in Rockefeller Center, with 70 stories, 850 ft (259 m) high. The former World Trade Center, which was the tallest building in the city until it was destroyed (Sept., 2001) by a terrorist attack, had two unstepped, rectangular towers of 110 stories each, one 1,362 ft (415 m) and the other 1,368 ft (417 m) high.