The entire square footage of all glass portions of a storefront is referred to as the "Area of Window." The Area of Window should be calculated by multiplying the overall width of the window by the height. For example, if the window is 30 feet wide and 40 feet tall, its Area of Window is 1,200 square feet. An alternative method for calculating the Area of Window is to add up the areas of all the individual squares made by projecting each corner of the window onto the floor. For example, if the window is 20 feet wide and 30 feet tall, its Area of Window is 420 square feet using this method. The two methods are equivalent but the first method is easier to calculate with tools such as a calculator or spreadsheet program. As you can see, the Area of Window is larger than the actual size of the window because it includes parts of the wall that aren't visible from outside the building. A store owner who wants to show off their merchandise may also want to include a display area in their calculation. If so, they should divide the total Area of Window by 2 to get the actual usable window space. In general, the Area of Window should be divided by 2 to find the usable window space.