The original World Trade Center Twin Towers each had 110 floors, which corresponds to 110 flights of stairs per tower

. This is why 9/11 stair climb memorial events typically involve climbing 110 flights, symbolizing the ascent of the towers

. To summarize:

• Each Twin Tower had 110 floors.
• Therefore, each tower had 110 flights of stairs.
• The North Tower was 1,368 feet tall; the South Tower was 1,362 feet tall

This number of flights was consistent for both towers until their destruction in 2001.