Building Height Explanation When a structure is stated as being 10 feet tall, it refers to the interior side wall height, often known as "leg height." Simply described, leg height is the point at the top of a building that is the shortest. For example, if a roof has 12-foot sloped walls, then the leg height would be 6 feet 6 inches. More commonly, the term "floor to ceiling" is used instead. This refers to the height from the floor to the highest point in the room, which will usually be the ceiling. When you add the door width to the door height, you get the overall height of the doorway. If the doorway is 48 inches wide and 30 inches high, its overall height is 78 inches. The distance between the floor and the center of the door opening determines how big the door has to be. A 2-inch gap between the floor and the bottom of the door opening allows for a 40-inch-wide door. A 4-inch gap requires a 32-inch-wide door. If you want to know the maximum weight that can be carried through a particular doorway, simply divide the door's opening width by 2.35 (for a 20/20 door balance). The resulting number is your carrying capacity in pounds. For example, if the doorway is 36 inches wide, it can carry up to 220 pounds.