How to Determine Freight Class: A Step-by-Step Guide
Step 1 - Measure dimensions and weight
Measure the length, width, and height of your shipment in inches, including packaging, pallets, and any crating or overhang. Then weigh the complete, packaged shipment in pounds. Accuracy here matters: carriers re-measure, and a few inches can change the class.
Step 2 - Calculate density
Convert the dimensions to cubic feet, then divide weight by volume:
Density (lbs/ft³) = Weight ÷ Cubic feet
Example: a 48 × 40 × 36 inch pallet weighing 500 lbs. Volume = (48 × 40 × 36) ÷ 1,728 = 40 ft³. Density = 500 ÷ 40 = 12.5 lbs/ft³.
Our Freight Class Calculator does this automatically - enter weight and dimensions and it returns the density and estimated class.
Step 3 - Match density to class
Look up your density on the freight class chart. In the example above, 12.5 lbs/ft³ falls in the 12-13.5 range, which corresponds to class 85. See Freight Class Explained for the complete density-to-class table.
Step 4 - Verify against the NMFC provision
Density gives an estimate, but the binding answer is the commodity's actual NMFC provision, which may fix the class regardless of density (for fragile, hazardous, or high-value goods). Look up the commodity in the NMFC Lookup, or pull the authoritative class programmatically with the NMFC API so your TMS always rates shipments correctly.
Frequently asked questions
How do I calculate freight density?
Divide the shipment weight (lbs) by its volume in cubic feet, where volume = (length × width × height in inches) ÷ 1,728.
Is freight class based only on density?
For most commodities, yes - density is the main driver. But some items have a fixed class set by the NMFC due to stowability, handling, or liability.
What happens if I use the wrong freight class?
The carrier can reclassify the shipment after inspection and bill the difference, often with an adjustment fee.
Related guides
Look it up or automate it
Search NMFC codes free, or integrate classification into your TMS via the API.