under 1 pcf · NMFC density scale
The rating for freight at under 1 pounds per cubic foot on the current 13-band NMFC density scale. Typically bagged insulation and other extremely light freight.
Class 400 is the top of the current density scale, for freight under 1 pcf. Class 500 is not on the scale at all, though an older density guideline mapped sub-1 pcf freight to it - which is why some free calculators still return 500 for very light freight. We tested that: see the calculator audit.
Worked example. A standard pallet: 48 × 40 × 48 in, 40 lb. That is 53.3 cu ft and 40 lb → 0.75 pcf → class 400. Run your own numbers →
Freight class runs from 50 (densest, cheapest per pound) to 400 on the current density scale. Class 400 is band 13 of 13.
Either side of this band: denser freight (1 - 2 pcf) rates class 300, which is cheaper.
The full table is on the freight class chart, and the calculator works out density and class from your dimensions, including multi-pallet shipments.