Freight class is the classification engine of LTL pricing. The National Motor Freight Traffic Association (NMFTA) maintains the National Motor Freight Classification (NMFC), which assigns specific classifications from Class 50 (densest, lowest cost) to Class 500 (least dense or most difficult to transport, highest cost) to thousands of commodity types.
The four factors used to determine freight class are density (pounds per cubic foot), stowability (can it be loaded safely with other freight?), handling (does it require special care?), and liability (is it high-value or particularly susceptible to damage?). Density is the dominant factor for most commodities.
The density-to-class relationship is roughly inverse: denser freight gets a lower (cheaper) class; less dense freight gets a higher (more expensive) class. A pallet of steel pipe at 30 pounds per cubic foot classifies at Class 50. A pallet of stuffed animals at 1 pound per cubic foot might classify at Class 300 or higher.
Accurate classification matters for two reasons: billing accuracy and claim vulnerability. If a shipper mis-classifies freight at a lower class than the NMFC specifies, the carrier has the right to re-weigh and re-class the shipment and issue a freight bill correction, adding cost after the fact. If a carrier discovers a misclassification after a damage claim, they may use the incorrect classification to dispute the claim.
For commodities not specifically named in the NMFC, density-based classification rules apply. An online density calculator — available through the NMFTA — is the starting point for commodities without specific NMFC entries.