Waste is another factor that should be considered when purchasing lumber. A Board Foot Calculator can give you the raw amount of wood required, while you can then add an appropriate allowance for waste. Lumber may contain knots, cracks, defects, or areas that cannot be used in the finished project. Cutting boards to size can also create additional waste. For simple projects, the extra amount may be relatively small, while rough or highly figured lumber may require more. Adding a reasonable waste allowance can help prevent material shortages during construction or woodworking.