How to Measure a Skyscraper

The What, Who, and How of Tall Buildings

a row of lighted skyscrapers against an evening sky, reflected in water
Downtown of Los Angeles at Sunset. Photo by Shabdro Photo/Moment/Getty Images

Defining tall buildings and measuring height can be a slippery slope. One definition states that a skyscraper is a "very tall building having many stories." That's not much help. The answer to the question What is a skyscraper? is more complicated than you may think.

How tall is One World Trade Center? Late in 2013 the Council on Tall Buildings and Urban Habitat ruled that the spire atop 1WTC is an integral part of its architecture, which makes the whole building 1,776 feet high. Well, maybe. Let's consider how tall is tall.

low angle view, looking up to the towered top of the Burj Khalifa Tower
Burj Khalifa Tower, Dubai, United Arab Emirates. Photo by Holger Leue/Lonely Planet Images/Getty Images (cropped)

A skyscraper's height rank can change from year to year, month to month, and sometimes even day to day. This is nothing new. In May of 1930 the building at 40 Wall Street in New York City was the tallest building in the world—until the Chrysler Building topped out later that month. These days, to even make the list of top 100 highest, a building has to be over 1,000 feet. What building will top the 2,717 feet high Burj Khalifa in Dubai? More »

The CTBUH Ranks Skyscrapers

an architect presents his design to a row of men in chairs
Architect David Childs Explains the Design Vision of 1 WTC to the CTBUH Height Committee. Press photo ©2013 CTBUH (cropped)

In ancient times, decisions were made by people in power—a king would make a declaration, and it would be the law of the land. Today in the US many decisions are based on the model of the American legal system—rules (like laws) are developed, agreed upon, and then applied. But, who decides?

Since 1969, the Council on Tall Buildings and Urban Habitat (CTBUH) has been widely recognized as the judge for ranking skyscrapers. The organization, founded by Lynn S. Beedle and originally called the Joint Committee on Tall Buildings, has created and published criteria (the rules) for measuring height. CTBUH then evaluates and applies the criteria to individual buildings.

Sometimes CTBUH needs convincing before making a ruling. In 2013, architect David Childs traveled to Chicago to present evidence to the CTBUH Height Committee. Childs' presentation helped make the case for a ruling on the architectural height of One World Trade Center.

Three Ways to Measure Skyscraper Heights

An aerial view of the top of One World Trade Center and its spire
Above the Spire of 1WTC. Photo by Drew Angerer/Getty Images

The original design height of One World Trade Center (Freedom Tower) was a symbolic 1776 feet. David Childs' redesign of 1WTC accomplished this height with a spire and not with occupied space. Does the spire count? How is height measured? The Council on Tall Buildings and Urban Habitat (CTBUH) categorizes structural height in three ways:

  1. Architectural Top: Includes permanent spires, but not functional or technical equipment, such as antennae, signs, flag poles, or radio towers that can be removed or replaced
  2. Highest Occupied Floor: Height to the top space used by occupants, other than areas for servicing mechanical equipment
  3. Highest Point of the Building: Height to the tip of the top, no matter what it is. However, the structure has to be a building. A tall building must have at least 50% of its height occupied as usable, habitable space. Otherwise, the tall structure may be considered a tower for observation or telecommunications.

When ranking the height of skyscrapers, CTBUH considers architectural height and measures a building's height from "the lowest, significant, open-air, pedestrian entrance." Other people or organizations may argue that buildings are to be used by people and should be ranked by the highest Occupied Space. Still others may say that height is simply from the bottom to the top—but then do you exclude underground floors?

Tall, Supertall, and Megatall

the very tall one world trade center amongst the skyscrapers of lower manhattan in new york city
1WTC Dominates the New York City Skyline. Photo by Siegfried Layda/Getty Images (cropped)

The Council on Tall Buildings and Urban Habitat has established definitions that can be used as a starting point for discussing skyscrapers:

  • Tall: "a building of perhaps 14 or more stories – or over 50 meters (165 feet)"
  • Supertall: a building over 984 feet (300 meters)
  • Megatall: a building over 1,968 feet (600 meters)

The CTBUH acknowledges that counting the number of stories is a poor way to establish height, because floor-to-floor height is inconsistent among buildings. Nevertheless, the organization provides a Height Calculator to estimate height when the number of stories is known.

Although height may be a statistic made within certain criteria, tallness is relative to location and time period. For example, a silo is tall on a farm, and the first skyscraper built in 1885 would not be called tall today—The Home Insurance Building in Chicago was only 10 stories high!

Birth of the Skyscraper

View of the Farwell Building on Washington Street after the Great Chicago Fire, Chicago, Illinois, 1871
Farwell Building, Chicago, Illinois, 1871. Photo by Jex Bardwell/Chicago History Museum/Getty Images (cropped)

Today's skyscrapers evolved from a certain period of American history when just the right people, places, and things came together at the same time.

Need: After the Great Chicago Fire of 1871, the city needed to rebuild with more fire-resistant materials.
Materials: The Industrial Revolution was filled with inventors, including Bessemer who found a way to make a fire hot enough to turn iron ore into a new strong compound called steel.
Engineers: Builders became aware of new construction materials like steel. They had to have the idea of how to use new materials. Structural engineers determined that steel was strong enough to be used as a frame for an entire building. Thick walls were no longer necessary to hold up a building's height. The new type of structural design became known as skeleton construction.
Architects: Although William LeBaron Jenney may have been the first to successfully experiment with skeleton frame construction to build tall buildings (see The Home Insurance Building, 1885), many people consider Louis Sullivan to be the designer of the modern skyscraper. Many architects and engineers were experimenting with new designs and new construction methods. This group of forward-thinking designers was collectively called the Chicago School.

Skyscraper Wars

A view of Chicago's skyline at sunset from the 94th floor of the John Hancock Observatory
Chicago, Illinois, Birthplace of the Skyscraper. Photo by Phil/Moment/Getty Images (cropped)

Judging what is the tallest may not be as easy as you think.

New York City's One World Trade Center has an architectural height of 1776 feet (541.3 meter) and is 1792 feet (546.2 meters) to the very top tip. Chicago's Sears Tower, now called the Willis Tower, has an architectural height of 1451 feet (442.1 meter) and is 1729 feet (527.0 meter) high to its tip. Clearly, the tallest building in the US is 1WTC.

BUT....

The Willis Tower has an occupied height of 1354 feet (412.7 meter), higher than the 1268 feet (386.6 meters) of occupied space of 1WTC. So, why isn't the Chicago skyscraper the tallest building in America? The CTBUH uses architectural height to rank skyscrapers.

Still, many people argue that building space is what really counts. What do you think?

Activity:

You have been selected to decide the definition for the word "skyscraper." What is your definition? Defend or give a good argument as to why your definition is a good one.

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Craven, Jackie. "How to Measure a Skyscraper." ThoughtCo, Sep. 6, 2017, thoughtco.com/skyscraper-tall-buildings-deconstructed-177330. Craven, Jackie. (2017, September 6). How to Measure a Skyscraper. Retrieved from https://www.thoughtco.com/skyscraper-tall-buildings-deconstructed-177330 Craven, Jackie. "How to Measure a Skyscraper." ThoughtCo. https://www.thoughtco.com/skyscraper-tall-buildings-deconstructed-177330 (accessed October 19, 2017).