The usable floor area is 1,133,428 square feet, but there are bigger skyscrapers in Texas. These are all the ones I could find with 1 million+ square feet.
JP Morgan Chase Tower - Houston - 2,243,013 square feet
Bank of America Plaza - Dallas - 1,844,000
Wells Fargo Plaza - Houston - 1,833,760
Renaissance Tower - Dallas - 1,731,000
Comerica Bank Tower - Dallas - 1,531,000
Fulbright Tower - Houston - 1,483,988
Williams Tower - Houston - 1,483,308
Enterprise Plaza - Houston - 1,459,000
Santander Tower - Dallas - 1,410,300
CenterPoint Energy Plaza - Houston - 1,399,986
First National Bank Tower - Dallas - 1,399,986
TC Energy Cener - Houston - 1,399,308
1700 Pacific - Dallas - 1,344,760
Chase Tower - Dallas - 1,296,400
BG Group Place - Houston - 1,262,865
One Shell Plaza - Houston - 1,226,000
Fountain Place - Dallas - 1,200,000
Heritage Plaza - Houston - 1,149,596
6 X Guadalupe - Austin - 1,133,428
Trammel Crow Center - Dallas - 1,128,327
1600 Smith Street - 1,097,960
609 Main - Houston - 1,058,200
777 Main Plaza - Fort Worth - 1,025,252
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