Tallest steel building

Willis Tower in Chicago, Illinois, USA, is a 442 m (1,451 ft) tall, 108-story office skyscraper constructed from steel, and weighing 201,848 tonnes (222,500 tons) in total. The design incorporates nine steel-unit square tubes in a 3 x 3 tube arrangement, with each featuring a 22 x 22 m (75 x 75 ft) footprint. Completed in 1974, it has 423,637 m² (4.56 million ft²) of floor space.