As a result, we can claim with certainty that the Pentagon is the size of 138.2575 football fields and that the Burj Khalifa is the height of 9.0733 football fields set end to end. That's more than twice as tall as the Sears Tower, which at 2333 feet is almost as tall. The estimate for the length of the Pentagon is actually closer to 270 yards (240 meters). The actual length of the building is 295 feet (92 m), but some of this is taken up by entryways and elevators so it is usually considered as a distance between pillars rather than a perimeter fence. The Pentagon was built in 1772 as a military barracks in Washington D.C. In 1800, after nine years of construction, it was completed. Today, it is used by the United States Department of Defense.