The world's tallest skyscrapers tower above cities around the world. Eight of the 10 tallest are scattered throughout the Middle East and Asia in cities including Dubai, Taipei and Hong Kong. Two are in the United States , the Willis Tower in Chicago and One World Trade Center in New York.

On Tuesday, an international panel of architects announced that the monument to those killed in the Sept. 11 attacks would become the tallest building in the United States, surpassing Chicago's skyscraper.

The Council on Tall Buildings and Urban Habitat ruled that the needle atop One World Trade Center can be counted when measuring the structure's height, also making it the third tallest building in the world when it is completed.

Ranking these tall buildings, and the rest of the world's tallest structures, is more mind-bending than one might think.

Lists can vary depending, for example, on whether you count the broadcast antennas on top or whether you're judging them by highest usable floor.

Dubai's Burj Khalifa is the tallest building in the world at 2,717 feet.