To make calculating density and freight classes easier, there are a host of tools for automating the process. Also, most technology forward freight companies have tools embedded in their Transportation or Freight Management Software to make the process as easy as possible. This is especially helpful when you are shipping multiple items with different densities.
https://www.freightclasscalc.com/calculator.php
Once the proper densities
have been calculated your preferred freight provider should be able to help you
establish the most correct freight classes.
Generally, this is done with the use of freight classification sites
like http://www.nmfta.org/ and their website Class IT. Anyone can get a subscription to these online
services, but if your freight provider is knowledgeable and helpful, they
should be able to do this for you quickly.