I want to know how tall a building is by knowing how many floors are in it.I know this may vary from building to building, so specifically, how tall were the floors in the World Trade centers (twin towers)?
A floor is approximately 10 feet.
Not only do floor height (which is measured from top of floor to top of floor) vary by building, they also vary from floor to floor, based upon slab thickness, the purpose of the floor, and the location of the floor within the overall tower in terms of which story it is. Per Wiki, the height to the last floor was 1355ft, with 110 floors, which averages out to be 12.32 (or 12 feet, 4 inches) per floor, which sounds about right to me.
