The National Motor Freight Traffic Association (NMFTA) publishes a list of freight class designations, codes, and subclasses for commonly shipped items (https://classit.nmfta.org/). A subscription fee is required to access this list. You can learn more about freight classes from the experts at Koho for free on our freight classes pages.
Every commodity has both a freight class and a NMFC code. Freight class represents a category of items while NMFC codes relate to specific commodities within each of the 18 freight classes.
Density is the relationship between weight and size. A ping pong ball, which is very little material surrounding a good amount of air, is low density. Bricks, which are heavy for their size, are high density. In LTL shipping, it is commonly measured in pounds per cubic foot.