Why freight under 4 PCF costs what it does
An LTL carrier sells two things on a trailer: floor space and payload. A 53-foot dry van holds roughly 3,800 to 4,000 cubic feet and around 44,000 lbs. If you divide one by the other, a trailer is "balanced" at about 11 PCF. Freight far below that number fills the trailer long before it fills the payload, so every pound of it has to pay for a lot of air. The NMFC density scale prices that reality: the lower the density, the higher the class and the higher the rate per hundredweight.
The three bottom subprovisions cover everything under 4 PCF:
| Sub | Class | Density | Typical freight |
|---|---|---|---|
| 1 | 400 | under 1 PCF | Expanded polystyrene shapes, empty plastic containers, assembled lightweight displays |
| 2 | 300 | 1 to under 2 PCF | Fiberglass insulation, assembled wicker and resin furniture, empty rotomolded tanks |
| 3 | 250 | 2 to under 4 PCF | Mattresses, spiral and rectangular ductwork, upholstered seating, kayaks |
The commodity list is a guide, not a rule. Two pallets of the same duct fittings can land in different classes depending on how tightly they are nested. The scale only cares about the weight and the cube you hand the carrier.
The class itself is only half the cost. Light freight also tends to be tall, fragile on top, or both, which brings in the second problem: carrier cubic capacity rules that ignore your class entirely once the shipment is big enough.
Where the cube rules take over
Every major LTL carrier publishes a rules tariff item for low-density, high-cube shipments. The thresholds are close to each other and are summarised on the carrier cube rules guide:
- Tier 1: 350 cubic feet or more at under 3 PCF. Used by XPO (CNWY 199 Item 233), Saia (SAIA 170 Item 111), ABF (ABF 111 Item 616 / 611) and Estes (EXLA 105).
- Tier 2: 750 cubic feet or more at under 6 PCF. Used by essentially every national carrier, including Old Dominion (ODFL 100 Item 610-1), FedEx Freight, R+L and TForce.
- Height imputation: units marked do-not-stack, or taller than about 60 inches, are cubed at the 96-inch trailer ceiling, so their tariff cube is higher than their physical cube.
Look at what that means for this cluster. Anything in class 400, 300 or 250 is under 4 PCF, so it is always under the 6 PCF Tier 2 line, and class 400 and 300 freight is always under the 3 PCF Tier 1 line. The only question is size. Five ordinary pallets of class 300 freight at 70 inches tall already exceed 350 cubic feet. Once a rule applies, the carrier rates the shipment on a synthetic weight, usually 6 lbs per cubic foot of tariff cube, or on a cubic minimum charge, and the discount in your pricing agreement may not apply. Carriers reissue rules tariffs; the current issue of each carrier's tariff governs.
Test a low-density load against XPO Item 233
- Safe — tariff cube, density and linear feet stay under the carrier's cube and linear-foot rules.
- Tier 1 — 350 cu ft or more under 3 PCF (XPO, Saia, ABF, Estes): synthetic weight of 6 lbs per tariff cubic foot.
- Re-bill — 750 cu ft or more under 6 PCF, or linear feet at the carrier's rule: book volume LTL or direct partial truckload.
Worked example: ten pallets of spiral duct fittings
An HVAC fabricator ships ten 48 × 40 pallets of duct fittings, each 70 inches tall and 260 lbs, marked do-not-stack because the fittings would crush. Lane is about 1,100 miles on XPO.
| Step | Math | Result |
|---|---|---|
| Physical cube per pallet | 48 × 40 × 70 ÷ 1,728 | 77.78 cu ft |
| Physical cube, 10 pallets | 77.78 × 10 | 777.8 cu ft |
| Weight | 260 × 10 | 2,600 lbs |
| Actual density and class | 2,600 ÷ 777.8 | 3.34 PCF, class 250 |
| Tariff cube at 96 in | 48 × 40 × 96 ÷ 1,728 × 10 | 1,066.7 cu ft |
| Phantom cube added | 1,066.7 − 777.8 | 288.9 cu ft |
| Tariff density | 2,600 ÷ 1,066.7 | 2.44 PCF |
| Synthetic weight | 1,066.7 × 6 lbs | 6,400 lbs |
| Linear feet | 5 rows × 48 in ÷ 12 | 20 LF |
The load hits both XPO tiers (1,066.7 cubic feet is over 350 at under 3 PCF and over 750 at under 6 PCF) and 20 linear feet is past the 12-foot linear rule. The carrier now rates 6,400 lbs instead of 2,600. On our indicative cost model that moves the bill from about $1,281 at class 250 to about $2,114 under the cube rule. A direct partial truckload priced on 20 linear feet comes in near $1,444 and a spot volume LTL quote near $1,258, with no imputation and no inspection fee. These are planning figures, not quotes; your contract rates and the day's market decide the real ones.
Same pallets, lighter product, same outcome. At 150 lbs per pallet the load is 1.93 PCF and class 300; at 70 lbs per pallet it is 0.90 PCF and class 400. In both cases the synthetic weight is still 6,400 lbs, because the rule is driven by the 1,066.7 cubic feet of tariff cube, not by what is inside.
How close each load is to the next class
At the bottom of the scale the bands are narrow, so small changes cross them. For the ten-pallet example above:
| Pallet weight | Density | Class | To reach next tier |
|---|---|---|---|
| 70 lbs | 0.90 PCF | 400 | +78 lbs total, or 7 in less height, reaches class 300 |
| 150 lbs | 1.93 PCF | 300 | +56 lbs total, or 2.5 in less height, reaches class 250 |
| 260 lbs | 3.34 PCF | 250 | +512 lbs total, or 11.5 in less height, reaches class 175 |
The class 300 load is 56 lbs from class 250. That is the weight of one extra carton per two pallets, or a few inches of void fill taken out. The class 250 load needs 11.5 inches off every pallet to reach 4 PCF; that would bring the pallets to 58.5 inches, under the 60-inch line, but because they are marked do-not-stack they would still be cubed at 96 inches. Height reduction only removes the imputation if the top can carry weight.
Packaging fixes that move the density
On low-density freight the fix is almost always cube, not weight. In rough order of payback:
- Nest, telescope or knock down. Duct fittings nested by size, chairs stacked seat-in-seat, shelving shipped flat. Nesting can double density without adding a pound.
- Build a load-bearing top. A sheet of plywood or a corrugated tier sheet over a level top can make a pallet stackable. Stackable freight under 60 inches is cubed at its real height. The economics are covered on crated vs. palletized freight.
- Cut overhang and air. One inch of overhang on each side of a 48 × 40 pallet adds about 9 percent to its cube. See the overhang guide.
- Consolidate partial pallets. Three half-height pallets of the same item cost more cube than one full one because each carries its own deck and its own imputed space.
- Compress where the product allows. Roll-packed mattresses, compressed insulation and vacuum-packed foam change class outright.
Write the new dimensions on the bill of lading exactly as built. A good fix ruined by stale numbers on the BOL still gets a re-bill; the BOL checklist walks through it.
When to stop fixing the pallet and change the mode
Some freight cannot be made dense. A rotomolded tank is a rotomolded tank. Once a low-density shipment passes about 350 cubic feet of tariff cube, or 10 to 12 linear feet, the class-rated LTL bill stops being the reference price, and the comparison becomes LTL-with-penalty against modes that price space directly:
- Spot volume LTL prices the shipment on linear feet and weight as a space-filler. It still crosses terminals, so fragile light freight carries damage risk.
- Direct partial truckload keeps the freight on one trailer from pickup to delivery, with no cross-dock and no height imputation. For tall, light, non-stackable pallets this is usually the clean answer; see direct partial truckload.
- A 26-foot box truck fits 12 single-stacked GMA pallets, which covers most low-density loads up to about 1,650 cubic feet on regional lanes.
If you want both prices side by side for a real load, send the dimensions, weights, stackability and ZIPs to rates@cubictransport.com.
