Today was extremely slow at work, and I love architecture, so I sat around figuring out the square footage of the Sears Tower. ([SEARS TOWER]) Here is all the calculations broken down into groups. What I know is that the Sears Tower was built in a "tube" design, consisting of 9 individual tubes built together to form this building. Each tube is 75' x 75' in diameter. At several stages in the building, tubes will taper off. Two tubes end at the 50th floor, two more tubes end at the 66th floor, and 3 more tubes end at the 90th floor, leaving the last remaining two tubes to reach the full height to the 110th floor. Here is a paint drawing I did to help visualize the building. http://i93.photobucket.com/albums/l42/TheOriginalJames/SearsTowerDiagram.jpg I broke this down into four groups consisting of; Floors 1-50 Floors 51-66 Floors 67-90 Floors 91-110 Floors 1-50 occupy 3 tubes by 3 tubes, or 225x225 giving a total footprint of 50,625 sq ft. ~ 50 floors * 50,625 sq ft gives you a total of 2,531,250 sq ft. Floors 51-66 lose two tubes, giving a total footprint of 39,375 sq ft. ~ 16 floors * 39,375 sq ft gives you a total of 630,000 sq ft. Floors 67-90 lose two more tubes, giving a total footprint of 28,125 sq ft. ~ 24 floors * 28,125 sq ft gives you a total of 675,000 sq ft. Floors 91-110 lose three more tubes, giving a total foot print of 11,250 sq ft. ~ 20 floors * 11,250 sq ft gives you a total of 225,000 sq ft. If you add all these totals together you get a Total square footage of the above ground building at 4,061,250 square feet. Referencing the site provided above, and looking at wiki (Sears Tower - Wikipedia, the free encyclopedia) on the Sears Tower, it totals the square footage at 4.56 million sq ft. Now with 104 elevators, electrical rooms, closet spaces, hallways, restaurants, skydeck, etc... the Rentable Square Footage (RSF) is only 3.8 million sq ft. *only...?* Taking into consideration that there are three underground levels that encompass the entire footprint, (50,625*3 = 151,875 sq ft), this still only brings up the total square footage to 4,213,135 sq ft of space. Does anyone know where the other 286,865 sq feet are? Or did I do something incorrectly here? There is no other helpful information that I can find.