That last column is the one that reaches the invoice. A carrier bills the weight it scales, pallet included, so the tare is freight you pay for and did not sell. On a 500-pound shipment a 40-pound pallet is 8 percent of the billed weight and 8 percent of the density that sets the class.
Forty pounds is not rounding
The number looks like noise next to a shipment, and on a full truckload it is. On an LTL shipment it is not, for a reason that has nothing to do with density: carriers reweigh, and the tolerance band on a declared weight is commonly 20 pounds. A 40-pound pallet left out of the declared weight puts the shipment 40 pounds light, which is twice the tolerance, so the scale flags it before anyone argues about class. The fee is small and the reclassification that follows is not.
Three numbers on one stack
Take cartons stacked 48 inches tall on a 48 × 40 pallet, 620 pounds of product.
The carton cube is 48 × 40 × 48 = 92,160 cubic inches, and 92,160 ÷ 1,728 = 53.33 cubic feet. 620 ÷ 53.33 = 11.63 pcf, which is class 92.5.
Add the 40-pound pallet to the weight and leave the cube alone: 660 ÷ 53.33 = 12.38 pcf, which is class 85. One pallet, one class, in your favour.
Now measure the way the carrier measures, floor to the top of the highest carton, which is 54.5 inches: 48 × 40 × 54.5 = 104,640 cubic inches, 60.56 cubic feet. 660 ÷ 60.56 = 10.90 pcf, and you are back at class 92.5.
The deck height takes back what the weight gives
Those two effects point opposite ways and almost cancel. The 40 pounds lift density by 6 percent; the 6.5 inches of deck lower it by 12 percent, because the deck is 12 percent of a 54-inch stack. So the class barely moves, and the case for getting the tare right is not the class at all — it is the weight on the bill of lading and the reweigh that follows when it is wrong.
This is also why a heavier pallet is not automatically worse. A 65-pound pool pallet adds 25 pounds of billed weight over a 40-pound stringer and, if it is a block pallet, sits about the same height, so the density change is small. What changes is the 25 pounds times every pallet on the load.
Which weight to declare
Weigh two empty pallets from the stack and average them, then write that number next to the piece count on the bill of lading. Do not use the catalogue figure, because moisture moves a wood pallet by ten pounds either way and a repaired pallet moves more. The deck height is part of the same written specification, and that is where the 48 × 40 empty weight and dimensions come from.
If the pallet is going to be in the cube anyway, put it in the density deliberately rather than discovering it at the scale.