HSN stands for Harmonized System of Nomenclature. It is a system for classifying commodities created by the World Customs organization. U.S. LTL shipping, however, uses NMFC classifications instead.
The National Motor Freight and Traffic Association has 18 freight classes numbered 50 to 500. The lower the freight class, the lower the cost of transporting that freight.
Multiply the length, width, and height of your shipment, then divide the total weight of your package by that number. If your shipment is 4 feet long, 5 feet wide, and 4 feet tall, you would multiply 4 x 5 x 4 to get 80 cubic feet. If it weighs 800 pounds, you would divide 800 / 80 to get 10 pounds per cubic foot.