The width of the average corner casing is about 5 inches, and the easiest and quickest way to estimate material for this purpose is to allow 1 foot board measure to each lineal foot in hight per corner. Thus the hight of a corner in feet gives the number of feet board measure required, and is very easy to calculate. For example, if a building has 18 feet studding for outside walls it will require 18 feet of lumber, board measure, per corner for corner casings. Many houses have what are commonly termed belt courses. These are usually casings of the same width as the corner casings and extend around the building at the top or bottom of the window and door frames. To estimate these, find the number of feet, lineal measure, required and divide by 2, which gives the amount in board measure. Board measure is understood to mean 1 inch thick. One quarter must be added for 1½-inch lumber, and one-half for 1½ inch lumber. In estimating corner casings and belt casings in the manner just described, nothing need be added for waste, because we have estimated the casings 6 inches wide when only 5 inches are required. This allowance is sufficient to cover the waste and makes the computation much easier.