The National Motor Freight Traffic Association (NMFTA) created the National Motor Freight Classification (NMFC). It is used for all interstate, intrastate, and foreign commercial movement of LTL cargo. NMFC codes provide standardized freight classes to determine the transportability of the large variety of commodities that are shipped together in LTL shipments every year.
If the couch you are shipping has not been assembled yet and you are shipping various components that you can use freight class 250. If you are shipping a complete product then you should use freight class 175.
No. While density is one of the primary factors in determining NMFC freight class, other factors, such as value, are also used in making that determination. Gold bars, for example, are very dense, but they fall into shipping class 500 along with very low-density items because of their high value.