Willis Tower, originally named the Sears Tower, is a 110-story supertall skyscraper in the West Loop neighborhood of Chicago, Illinois. It rises 442 meters (1,451 feet) to the roof and 527 meters (1,729 feet) including its twin antennas, making it the tallest building in Chicago and the third-tallest in the United States. From its completion in 1973 until 1998, it held the title of the world's tallest building, when it was surpassed by the Petronas Towers in Kuala Lumpur.
Where Is Willis Tower?
Willis Tower stands at 233 South Wacker Drive, at coordinates 41.8789°N, 87.6359°W, on the western edge of Chicago's Loop. The Loop is the city's central business district, named for the elevated train tracks that encircle it. The building rises on the west bank of the South Branch of the Chicago River, roughly 1.3 kilometers from the Lake Michigan shoreline.
Chicago's setting on a flat glacial plain gives the tower extraordinary prominence. With no surrounding hills or mountains to break the horizon, the building can be seen from distances exceeding 60 kilometers on clear days. Its position places it within walking distance of several major landmarks: Union Station lies about 0.5 km south, the Chicago Board of Trade Building 0.8 km southeast, and Millennium Park 1.5 km east along the lakefront.
The Geology Beneath the Tower
The ground that supports Willis Tower tells a story written during the last Ice Age. Chicago sits on a thick layer of clay-rich glacial till deposited by retreating ice sheets roughly 12,000 years ago. This soft soil cannot bear the immense weight of a supertall building on its own, so engineers anchored the tower with deep caisson foundations that descend to solid bedrock approximately 30 meters below street level.
This combination of flat prairie terrain and deep bedrock made Chicago an ideal birthplace for the skyscraper. The same conditions that produced the first steel-frame high-rises in the 1880s also allowed Willis Tower to climb higher than any building before it.
Engineering and Architecture
Willis Tower's defining innovation is its bundled-tube structural system, conceived by Bangladeshi-American structural engineer Fazlur Rahman Khan of the firm Skidmore, Owings & Merrill. Rather than relying on a single massive frame, the design uses nine square tubes, each measuring 22.9 meters per side, bundled together like a cluster of hollow columns. Together they act as a rigid vertical structure that resists Chicago's notorious winds.
The tubes do not all reach the same height, and this is what gives the tower its instantly recognizable stepped silhouette. Two tubes terminate at the 50th floor, two more at the 66th, and three at the 90th, leaving the final two to rise the full 110 stories. The result is a tapering profile that both looks dramatic and improves the building's aerodynamic performance.
The bundled-tube approach reduced the steel required by roughly a third compared with a conventional frame of the same height. Even so, the building contains around 76,000 tonnes of steel, enough concrete to pave an eight-lane highway 8 kilometers long, and about 16,000 bronze-tinted windows set in a black aluminum skin. In strong winds, the upper floors can sway as much as 15 centimeters from center, a movement carefully engineered to keep the structure safe and comfortable.
History and Significance
Sears, Roebuck and Company commissioned the tower in 1969 to consolidate some 350,000 employees scattered across Chicago into a single headquarters. Construction finished on May 3, 1973, under lead architect Bruce Graham, and the new tower immediately surpassed the World Trade Center as the world's tallest building, a title it would hold for 25 years.
Sears moved out in 1992, and the building lived on under its original name for years afterward. In 2009 the British insurance broker Willis Group acquired the naming rights, prompting the change to Willis Tower, a name many longtime Chicagoans still resist in favor of "Sears Tower."
The building's deeper legacy lies in Fazlur Rahman Khan's engineering. His tubular structural concepts proved that extreme height could be achieved economically, and they shaped nearly every supertall building that followed, from the Burj Khalifa in Dubai to One World Trade Center in New York. Khan is buried in Chicago's Graceland Cemetery and is widely honored as the "father of tubular design."
The Skydeck and the Ledge
The Skydeck observation deck on the 103rd floor sits 412 meters (1,353 feet) above street level and draws roughly 1.7 million visitors each year. On clear days, the view stretches up to 80 kilometers and spans four states: Illinois, Indiana, Wisconsin, and Michigan. Visitors can trace the curve of Lake Michigan's shoreline, follow the branching Chicago River, and watch the prairie fade into the western horizon.
The deck's most famous feature is the Ledge, a set of four retractable glass-floor balconies installed in 2009. Each box extends 1.3 meters out from the building's facade, leaving visitors suspended over a sheer drop to Wacker Drive far below. The balconies are built from half-inch-thick laminated glass and each can support up to 5 tonnes, but standing on the transparent floor remains a genuinely vertigo-inducing experience.
Key Facts
- Roof height: 442 m (1,451 ft); 527 m (1,729 ft) with antennas
- Floors: 110
- Completed: May 3, 1973
- Architect / Engineer: Bruce Graham / Fazlur Rahman Khan, Skidmore, Owings & Merrill
- Structural system: Bundled tube of nine square tubes
- Skydeck: 103rd floor, 412 m, with the glass-floored Ledge
- World's tallest building: 1973–1998
Frequently Asked Questions
How tall is Willis Tower?
Willis Tower stands 442 meters (1,451 feet) to its roof and 527 meters (1,729 feet) including its twin rooftop antennas. It is the tallest building in Chicago and currently the third-tallest in the United States.
Why is it called Willis Tower instead of Sears Tower?
The building was named the Sears Tower after Sears, Roebuck and Company, which built it as its headquarters in 1973. Sears left in 1992, and in 2009 the insurance broker Willis Group bought the naming rights, changing the name to Willis Tower. Many Chicagoans still call it the Sears Tower.
Can you see four states from the Skydeck?
Yes. On clear days the view from the 103rd-floor Skydeck reaches up to 80 kilometers, allowing visitors to see parts of Illinois, Indiana, Wisconsin, and Michigan, along with Lake Michigan and the surrounding prairie.
What makes the Willis Tower design special?
Its bundled-tube structure, made of nine square tubes that stop at different heights, was a breakthrough by engineer Fazlur Rahman Khan. It used far less steel than a conventional frame while resisting strong winds, and it influenced supertall skyscrapers worldwide.
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