How tall is the Willis Tower?

How tall is Willis Tower?

Willis Tower in Chicago stands 442.3 m (1,451 ft) to its main roof, the height used on this site. CTBUH, which maintains the official world rankings, lists the architectural height as 442.1 m (1,451 ft), and the two pairs of broadcast antennas on the roof take the tip to 527 m (1,729 ft). The building has 108 full floors by CTBUH's count, although the owners describe it as 110 stories.

For 25 years after its completion in 1973, Willis Tower, then the Sears Tower, was the tallest building in the world. Today it is the third-tallest building in the Western Hemisphere, after One World Trade Center and Central Park Tower in New York, and still the tallest in Chicago. Compare it with other skyscrapers in the 3D height comparison tool.

Why there are three different heights

CTBUH measures every building from the level of its lowest significant pedestrian entrance, then offers three endpoints: the architectural top, the highest occupied floor, and the tip. Spires count toward architectural height; antennas do not, because they are classed as equipment that can be added, extended or removed.

Willis Tower is a textbook example of why the distinction matters. Its roof is flat, with no spire, so its architectural height equals the roof height, 442.1 m. The two antenna masts were added in 1982, raising the tip to 520 m, and the western antenna was extended in 2000, taking the tip to its current 527 m. Neither change affected the official height, because antennas are excluded.

That rule shaped one of the most famous disputes in skyscraper history. In 1996 the Council ruled that the decorative spires of the Petronas Towers in Kuala Lumpur were architectural, giving them an official height of 451.9 m, about 10 m above Willis Tower's roof. Chicago observers pointed out that Willis Tower's roof, top floor and antenna tips were all higher than the corresponding points of the Petronas Towers. The controversy led CTBUH to publish several categories of height for a time, and it is why the three-measurement system is still used today.

Floors: 108 or 110?

The building's owners advertise Willis Tower as 110 stories tall. CTBUH counts 108 floors above ground. According to Wikipedia's summary of the building's records, the owners count the main roof as the 109th level and the roof of the mechanical penthouse as the 110th. Neither is a full occupied floor, so CTBUH does not include them.

The original World Trade Center towers also had 110 stories, and for a time the Sears Tower and the Twin Towers formed an unusual trio of buildings with the same nominal floor count competing for the world height record. Sears Tower's roof was higher, which is why it took the title in 1973.

The bundled tube: how it was built

A structural innovation

The engineering behind Willis Tower is as famous as its height. The structural engineer Fazlur Rahman Khan and architect Bruce Graham of Skidmore, Owings & Merrill developed the bundled tube system: nine square steel tubes, each 75 by 75 ft (23 by 23 m), grouped in a three-by-three grid to form the 225 ft (69 m) square base.

Each tube is a rigid frame of closely spaced exterior columns that acts like a hollow beam standing on end, resisting wind loads efficiently. Bundling the tubes allowed them to brace each other, so the tower could reach record height using far less steel than a traditional frame would have needed.

The setbacks

Not all nine tubes run to the top. Two end at the 50th floor, two more at the 66th, and three at the 90th, leaving only two tubes rising to the full height. Those setbacks give the building its distinctive stepped silhouette, and they reduce wind loads high up by changing the shape the wind meets at different heights.

Construction

Construction began in 1970 for Sears, Roebuck and Co., then the largest retailer in the world, which wanted to consolidate its Chicago staff in a single headquarters. According to the building's owners, more than 2,000 workers built the tower, and it was completed in 1973. The frame used about 74,000 short tons (67,000 tonnes) of steel, and the project cost about US$150 million at the time.

The 1973 race for the world record

Willis Tower was born into one of the most intense periods of skyscraper competition. For more than 40 years the Empire State Building, completed in 1931, had held the world height record. Then, within about two years, it was overtaken twice.

First came New York's World Trade Center. Its North Tower topped out in 1970 and was completed in 1972 with a roof height of 417 m, ending the Empire State Building's long reign. Sears, Roebuck and Co. had already begun its Chicago headquarters, and the design took it higher still. When the Sears Tower was completed in 1973, its roof stood about 25 m above that of the North Tower, and Chicago, the city that had given the world its first skyscrapers in the 1880s, regained the title.

Willis Tower held the record for 25 years, longer than any building since the Empire State. When the Petronas Towers took the title, the dispute over spires versus roofs meant that many people in Chicago never accepted the change. The question became moot in 2004, when Taipei 101 surpassed both on every measure. The Twin Towers page covers the New York side of the story.

Fazlur Khan's legacy

The bundled tube was the culmination of a series of structural systems that Fazlur Rahman Khan developed at Skidmore, Owings & Merrill in the 1960s and 1970s. His key insight was that a tall building could be treated as a hollow tube cantilevered from the ground, with its exterior walls doing most of the work against wind. That idea, refined into framed, trussed and bundled tubes, made very tall buildings far more economical. Variants of the tube principle underpin many later supertall towers, including Burj Khalifa, also designed by SOM, whose buttressed core is often described as a descendant of the same thinking. Khan died in 1982; a statue of him stands in the lobby of Willis Tower.

Timeline: from Sears Tower to Willis Tower

The name change in 2009 followed a lease agreement with the London-based insurance broker Willis Group Holdings. Sears had already moved its headquarters out of the building in the 1990s. The rename was unpopular with many locals, and "Sears Tower" remains common in everyday Chicago speech.

Willis Tower compared with other skyscrapers

The Petronas Towers edge out Willis Tower by less than 10 m, entirely thanks to their spires. One World Trade Center is officially almost 100 m taller, but its roof, at 417 m, is about 25 m lower than Willis Tower's, and its observatory is also lower. Against New York's Empire State Building, Willis Tower wins by about 61 m. The building's owners describe it as the 12th-tallest building in the world, while CTBUH's current list ranks it 25th, a gap that reflects how quickly new supertall towers have been completed in Asia and the Middle East. Explore the full ranking in the tallest lists.

Visiting Skydeck Chicago and The Ledge

The Skydeck occupies the 103rd floor, 1,353 ft (412.4 m) above the street. Skydeck Chicago describes it as America's highest observation deck, and that claim holds because its floor is about 26 m higher than One World Observatory's in New York, even though One WTC is officially the taller building.

The best-known feature is The Ledge: four glass boxes that project 4.3 ft (1.3 m) from the west side of the building. The floor, walls and ceiling are made of 1.5 in (3.8 cm) of glass, so visitors stand with nothing beneath them but a 1,353 ft drop to Wacker Drive. The Ledge opened on 2 July 2009, shortly after the renaming.

Practical points from Skydeck Chicago and the building's owners:

• Skydeck is open 365 days a year; winter hours (October to February) are 9:00 to 20:00, extended to 21:00 on Saturdays. Last entry is 30 minutes before closing.
• On a clear day, the views extend up to 50 miles (80 km) and over four states: Illinois, Indiana, Michigan and Wisconsin.
• The entrance is on Jackson Boulevard; the building's main address is 233 South Wacker Drive.
• An exhibit on Chicago history, The Chicago Museum, is part of the route up to the deck.

Putting 442 meters in perspective

• Willis Tower's roof is about 253 times the height of a 175 cm (5′9″) adult.
• Its antennas reach 527 m, only 14 m less than One World Trade Center's architectural height.
• Stacking four-and-a-half Big Bens (96 m each) would reach the roof.
• The base, at 69 m square, is wider than the copper figure of the Statue of Liberty is tall; with pedestal and foundation she reaches 93 m.

For more buildings, visit the landmarks hub, or convert any of these figures between meters and feet with the height converter.