The world's tallest structure is the tall Burj Khalifa in Dubai, United Arab Emirates. The building gained the official title of "Tallest Building in the World" at its opening on 4 January 2010. It is taller than any other man-made structure ever built.

The Council on Tall Buildings and Urban Habitat, an organization that certifies buildings as the "World’s Tallest", recognizes a building only if at least fifty percent of its height is made up of floor plates containing habitable floor area. Structures that do not meet this criterion, such as the CN Tower, are defined as "towers".

There are dozens of radio and television broadcasting towers which measure over 600 metres (about 2,000 ft) in height, and only the tallest are recorded in publicly available information sources.

Debate over definitions

When assessing the placings of structures, there is some debate about:

• whether structures under construction should be included in the list

• should a building or structure have to be officially opened before it is included on the list.

• whether structures rising out of water should have their below-water height included.

• what should be counted as a building or a tower, and what is being measured.

• for towers, whether guy-wire-supported structures should be counted.

For buildings, there is debate over:

• whether only habitable height is considered

• whether communication towers with observation galleries should be considered "habitable" in this sense

• whether rooftop antennas, viewing platforms or any other architecture that does not form floors, walls and rooms, i.e. not built as an occupiable room, should be considered towards height of building

• what would stop a room built on top of a telecommunications or viewing tower from changing the tower's class to that of "building"

• why a building that is not officially opened should be excluded from the ranks of tallest buildings

• what counts as an official opening

Tallest structures

This category does not require the structure be "officially" opened.

The tallest man-made structure is Burj Khalifa, a skyscraper in Dubai that reached in height on 17 January 2009. By 7 April 2008 it had been built higher than the KVLY-TV mast in North Dakota, USA. That September it officially surpassed Poland's Warsaw radio mast, which stood from 1974 to 1991, to become the tallest structure ever built. Guyed lattice towers such as these masts had held the world height record since 1954.

The CN Tower in Toronto, Canada, standing at , was formerly the world's tallest completed freestanding structure on land. Opened in 1976, it was surpassed in height by the rising Burj Khalifa on 12 September 2007. It has the world's second highest public observation deck at .

The Petronius Platform stands off the sea floor leading some, including Guinness World Records 2007, to claim it as the tallest freestanding structure in the world. However, it is debated whether underwater height should be discounted in the same manner as height below ground is ignored on buildings. The Troll A platform is , without any part of that height being supported by wires. The tension-leg type of oil platform has even greater below-water heights with several examples more than deep. However, these platforms are not considered constant structures as the vast majority of their height is made up of the length of the tendons attaching the floating platforms to the sea floor. Despite this, Guinness World Records 2009 listed the Ursa tension leg platform as the tallest structure in the world with a total height of . The Magnolia Tension-leg Platform in the Gulf of Mexico is even taller with a total height of .
Taipei 101 in Taipei, Taiwan, was the world's tallest inhabited building in only one of the four main categories that are commonly measured: at as measured to its architectural height (spire). The height of its roof, , and highest occupied floor, , had been overtaken by the Shanghai World Financial Center with corresponding heights of and respectively. Willis Tower (formerly Sears Tower) was highest in the final category: the greatest height to top of antenna of any building in the world at .

Burj Khalifa broke the height record in all four categories for completed buildings by a wide margin. The Shanghai World Financial Center had the world's highest roof, highest occupied floor, and the world's highest public observation deck at . It retains the latter record, as Burj Khalifa's official observation deck will be at .

Tallest structure by category

Due to the disagreements over how to measure height and classify structures, engineers have created various definitions for categories of buildings and other structures. One measure includes the absolute height of a building, another includes only spires and other permanent architectural features, but not antennas. The tradition of including the spire on top of a building and not including the antenna dates back to the rivalry between the Chrysler Building and 40 Wall Street. A modern-day example is that the antenna on top of Willis Tower (formerly Sears Tower) is not considered part of its architectural height, while the spires on top of the Petronas Twin Towers are counted.
Note: The following table is a list of the tallest structure in each of the categories below. There can only be one structure in each category, unless the title for the tallest is a draw.

Tallest destroyed structures by category, not surpassed by existing structures

There are some destroyed architectural structures which were taller than the tallest existing structure of their type.

Tallest building by function

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Tallest buildings

Up until 1998 the tallest building status was essentially uncontested. Counting buildings as structures with floors throughout, and with antenna masts excluded, Willis Tower (previously Sears Tower) in Chicago was considered the tallest. When the Petronas Twin Towers in Kuala Lumpur, Malaysia were built, controversy arose because the spire extended nine metres higher than the roof of Willis Tower. Excluding the spire, the Petronas Towers are not taller than Willis Tower. At their convention in Chicago, the Council on Tall Buildings and Urban Habitat (CTBUH) reduced Willis Tower from world's tallest and pronounced it not second tallest, but third, and pronounced Petronas as world's tallest. This action caused a considerable amount of controversy, so CTBUH defined four categories in which the world's tallest building can be measured:

• Height to Architectural Top (including spires and pinnacles, but not antennas, masts or flagpoles). This measurement is the most widely utilized and is used to define the rankings of the 100 Tallest Buildings in the World.

• Highest Occupied Floor

• Height to Top of Roof (omitted from criteria from November 2009 onwards)

• Height to Tip

The height is measured from the level of the lowest, significant, open-air, pedestrian entrance. At the time, the Willis Tower held first place in the second and third categories, the Petronas Towers held the first category and the original World Trade Towers held the fourth. Within months, however, a new antenna mast was placed on the Willis Tower, giving it hold of the fourth category.
On April 20, 2004, Taipei 101 in Taipei, Taiwan, was completed. Its completion gave it the world record for the first three categories. On July 21, 2007 it was announced that Burj Khalifa had surpassed Taipei 101 in height, reaching .

Since being completed in early 2010, Burj Khalifa leads in all categories (the first building to do so). With a spire height of , Burj Khalifa surpassed Taipei 101 as the tallest building to architectural detail and the Willis Tower as the tallest building to tip. It also leads in the category of highest occupied floor.

Before Burj Khalifa was completed, Willis Tower led in the fourth category with , previously held by the World Trade Center until the extension of the Chicago tower's western broadcast antenna in 2000, over a year prior to the World Trade Center's destruction in 2001. Its antenna mast included, One World Trade Center measured . The World Trade Center became the world's tallest buildings to be destroyed or demolished; indeed, its site entered the record books twice on September 11, 2001, in that category, replacing the Singer Building, which once stood a block from the WTC site.

Structures such as the CN Tower, the Ostankino Tower and the Oriental Pearl Tower are excluded from these categories because they are not "habitable buildings", which are defined as frame structures made with floors and walls throughout.

History of record holders in each CTBUH category

World's tallest freestanding structure on land

Freestanding structures include observation towers, monuments and other structures not generally considered to be "Habitable buildings", but excludes supported structures such as guyed masts and ocean drilling platforms.
(See also history of tallest skyscrapers.)
The world's tallest freestanding structure on land is defined as the tallest self-supporting man-made structure that stands above ground. This definition is different from that of world's tallest building or world's tallest structure based on the percent of the structure that is occupied and whether or not it is self-supporting or supported by exterior cables. Likewise, this definition does not count structures that are built underground or on the seabed, such as the Petronius Platform in the Gulf of Mexico. Visit world's tallest structure by category for a list of various other definitions.

As of 12 May 2008, the tallest freestanding structure on land is the Burj Khalifa in Dubai, United Arab Emirates. The building, which now stands at , surpassed the height of the previous record holder, the CN Tower in Toronto, Ontario, on September 12, 2007. It was completed in 2010, and was topped out at in January 2009.

History

The following is a list of structures that have held the title as the tallest freestanding structure on land. (See also Timeline of three tallest structures in the world until Empire State Building).

Diagram of the Principal High Buildings of the Old World, 1884.

Notable mentions include the Pharos (lighthouse) of Alexandria, built in the third century BCE and estimated between 115–135 m (383–440 ft). It was the world's tallest non-pyramidal building for many centuries. Another notable mention includes the Jetavanaramaya stupa in Anuradhapura, Sri Lanka, which was built in the third century, and was similarly tall at . These were both the world's tallest or second tallest non-pyramidal buildings for over a thousand years.

The tallest secular building between the collapse of the Pharos and the erection of the Washington Monument may have been the Torre del Mangia in Siena, which is tall, and was constructed in the first half of the fourteenth century, and the tall Torre degli Asinelli in Bologna, also Italy, built between 1109 and 1119.

World's highest observation deck

Timeline of development of world's highest observation deck since inauguration of Eiffel Tower.

Higher observation decks have existed on mountain peaks or cliffs, rather than on tall structures. For example, the Royal Gorge Bridge in Cañon City, Colorado, USA, was constructed in 1929 spanning the Royal Gorge at a height of above the Arkansas River.

Timeline of guyed structures on land

As most of the tallest structures are guyed masts, here is a timeline of world's tallest guyed masts, since the beginning of radio technology.

As many large guyed masts were destroyed at the end of World War II, the dates for the years between 1945 and 1950 may be incorrect. If Wusung Radio Tower survived World War II, it was the tallest guyed structure shortly after World War II.

Tallest structures, freestanding structures, and buildings

thumb|300px|Burj Khalifa compared to some other well-known tall structures.See also: Timeline of three tallest structures in the world
The list categories are:

• The structures (supported) list uses pinnacle height and includes architectural structures of any type that might use some external support constructions like cables and are fully built in air. Only the three tallest are listed, as more than fifty US TV masts have stated heights of 600–610 metres (1969–2000 ft).

• The structures (media supported) list uses pinnacle height and includes architectural structures of any type that are not totally built in the air but are using support from other, denser media like salt water. All structures greater than are listed.

• The freestanding structures list uses pinnacle height and includes structures over that do not use guy-wires or other external supports. This means truly free standing on its own or, in similar sense, non-supported structures.

• The building list uses architectural height (excluding antennas) and includes only buildings, defined as consisting of habitable floors. Both of these follow CTBUH guidelines. All supertall buildings (300 m and higher) are listed.

Notes:

• Seven buildings appear on the freestanding structures category list with different heights than of another category. This is due to the different measurement specifications of those lists.

• Only current heights and where reasonable target heights are listed. Historical heights of structures that no longer exist, for example, for having collapsed, are excluded.

Source:

Under construction

Numerous supertall skyscrapers are in various stages of proposal, planning, or construction. Each of the following are under construction and, depending on the order of completion, could become the world's tallest building or structure in at least one category:

• The Tokyo Sky Tree under construction in Tokyo's Sumida district, is expected to be tall. It will be a broadcasting tower to replace the old Tokyo Tower. Construction began in 2008 and completion is expected in 2011, with public access in the spring of 2012.

• The Shanghai Tower, under construction in Shanghai, next to the Shanghai World Financial Center and the Jin Mao Building, is expected to be . Completion is expected in 2014.

• The Pentominium, under construction in Dubai, is expected to be tall and have 120 floors. If completed, it would be the tallest all-residential building in the world. Construction began in 2007 and completion is expected in 2013.

• The Guangzhou TV & Sightseeing Tower, under construction in Guangzhou, China, is topped-out at . Construction began in November 2005 and completion is expected in 2010.

• The Chicago Spire (formerly Fordham Spire), under construction in Chicago, is expected to be and have 150 floors. If completed, it would surpass the CN Tower as the tallest freestanding building in North America, and would be the tallest all-residential building in the world. Construction began in June 2007 and completion is expected in early 2012, however, construction is on hold.Shelbourne Development. (2008, April 06). The Chicago Spire Achieves 30 Percent Sales. Retrieved June 14, 2008 from http://www.shelbournedevelopment.com/press_release.php?id=96

• The Abraj Al Bait Towers are under construction in Mecca, Saudi Arabia. The tallest tower is expected to be tall when completed in 2010, becoming second-tallest building in the world when completed. It will also be the largest building in the world with a floor area of and the tallest hotel in the world.

• The Jakarta Tower (Menara Jakarta) is on-hold in Jakarta, Indonesia. It is expected to be tall up to the antenna, thus may be tallest concrete tower. It was expected to be completed in 2012, but has been put on hold.

• One World Trade Center, currently under-construction in New York City, will be the tallest building in the United States and the Western Hemisphere. Also, it will become the world´s tallest all-office building. Its spire will top out at .

• The Keangnam Hanoi Landmark Tower, under construction in Hanoi, Vietnam is expected to be tall. It will be completed on time in 2010 to celebrate Hanoi's 1000 anniversary.

• The Federation Tower East, under construction in Moscow's International Business Centre, is expected to be tall. Construction began in 2003 and completion is expected in 2010.

Proposed

Many proposed structures have not yet been built, and many probably never will be built. See proposed tall buildings and structures for structures that have been or are being proposed.

See also

• List of tallest buildings in the world

• List of tallest structures in the world

• List of tallest freestanding structures in the world

• List of towers

• List of architects of supertall buildings