What a cubic capacity rule is and why carriers publish one
Class-rated LTL pricing assumes that weight and freight class together describe how much of a trailer your shipment uses. That holds for a dense skid of boxed hardware. It breaks down for a skid of spiral duct, empty plastic tanks or assembled cabinets, which can fill a quarter of a 53' trailer while weighing less than a single pallet of canned goods. The carrier still has to haul the space, and space is what it sells.
A cubic capacity rule closes that gap. Once a shipment crosses a published volume threshold while sitting under a published density, the carrier stops rating it on scale weight and rates it on a synthetic weight built from cube, or on linear feet of trailer floor, or on a flat cubic minimum charge. Most rules also restrict or void the FAK (freight all kinds, a single class negotiated for mixed freight) discount on the re-rated bill. That combination is what turns a planned $600 invoice into a $1,200 to $1,900 one.
Density (PCF) = total weight including pallets ÷ total cubic feet
Synthetic weight = tariff cubic feet × 6 lbs
Three mechanisms appear in almost every carrier's rules tariff, sometimes in the same item and sometimes in separate items:
- Cubic threshold with a density floor. The common pair is 350 cu ft at under 3 PCF and 750 cu ft at under 6 PCF. Some carriers publish only the 750 tier.
- Linear foot rule. When a shipment occupies 10 to 15 or more feet of trailer length, the carrier can rate it on floor space regardless of cube or density.
- Height imputation. A unit that cannot carry another unit on top, because it is labelled do not stack, has a cone or pyramid top, or stands over roughly 60 in, is measured as if it reached the 96 in trailer ceiling. That phantom cube is what pushes many modest shipments over the thresholds above.
Run your load against every carrier trigger at once
- 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.
The carrier matrix: triggers, items and penalty mechanics
The matrix below lists the rules tariff and item each carrier uses, the cube and density pair that triggers it, how non-stackable units are measured, and how the penalty is calculated. Each row links to a full breakdown with a worked example on the carrier page.
| Carrier | Rules tariff item | Cube / LF trigger | Height imputation | Re-rating mechanism |
|---|---|---|---|---|
| Old Dominion | ODFL 100 Item 610-1 | ≥ 750 cu ft under 6 PCF; ≥ 15 LF | Non-stackable or 48–60 in+ units cubed to 96 in | 6 lbs × cu ft at class 125/150 or minimum floor; FAK discount voided |
| XPO | CNWY 199 Item 233 | Tier 1 ≥ 350 cu ft under 3 PCF · Tier 2 ≥ 750 cu ft under 6 PCF | "Do not stack", cone-top or > 60 in cubed to 96 in | Cube × 6 PCF at applicable class with restricted discount, or flat cubic minimum |
| Saia | SAIA 170 Item 111 | ≥ 350 cu ft under 3 PCF or ≥ 750 cu ft under 6 PCF | Forced 96 in on non-stackable / irregular tops | Synthetic density weight floor + W&I inspection fee |
| FedEx Freight | FXF 100 series | ≥ 750 cu ft under 6 PCF, or 10–15+ LF | Over 60 in or non-stackable calculated at 96 in | Minimum density weight or linear-foot minimum charge |
| ABF Freight | ABF 111 Item 616 / 611 | ≥ 350 cu ft under 3 PCF or ≥ 750 cu ft under 6 PCF | Full trailer height (96–102 in) when top-loading restricted | 6 lbs/cu ft synthetic weight or cubic minimum schedule |
| Estes | EXLA 105 | ≥ 350 / ≥ 750 cu ft low-density; 12–15 LF | Non-stackable assessed full 96 in | Re-billed as capacity load / volume rate, contract discount stripped |
| R+L Carriers | RLCA 100 | ≥ 750 cu ft under 6 PCF or ≥ 12 LF | Full height imputed when freight cannot bear top weight | 750–1,000 lbs per LF synthetic floor + W&I correction |
| TForce Freight | UPGF 102 | ≥ 750 cu ft under 6 PCF | 96 in imputation on non-stackable skids | Synthetic weight adjustment + reclassification fee |
Summary of carrier rules tariff provisions as indexed by Cubic Transport. Carriers reissue rules tariffs; the current issue on the carrier's site governs any bill.
Read the matrix as three columns of risk, not one. A shipment can clear the cube trigger and still trip the linear foot rule; it can clear both on actual dimensions and trip both once the 96 in imputation is applied. The cubic feet and density calculator checks all three at once against the carrier you pick.
A few patterns hold across the table:
- The 350 cu ft tier is the stricter one for very light freight. XPO, Saia, ABF and Estes publish it. Old Dominion, FedEx Freight, R+L and TForce rely on the 750 tier plus a linear foot rule.
- Old Dominion's linear foot trigger is the loosest at 15 LF; most others sit at 12 LF, and the FedEx Freight provisions we reviewed run from 10 to 15 LF, so plan on the low end.
- Every carrier imputes the 96 in ceiling on units that cannot be stacked. The difference is only in how tall a unit must be before the carrier treats it as unstackable even without a label, usually somewhere between 48 and 60 in.
Why density class still matters after a rule fires
The NMFTA density scale assigns class from PCF. When a carrier imputes 96 in, the PCF it uses is the imputed one, which usually lands one or two tiers higher than your actual density. On some carriers the class follows the imputed density; on others the item names a fixed class for the synthetic weight (research on current issues shows Class 125 or 150 for the 6 PCF floor). Either way, the class you wrote on the bill of lading is no longer the class you are billed at.
| Sub | Density (PCF) | NMFC class | Typical commodities |
|---|---|---|---|
| Sub 1 | Less than 1 | 400 | Assembled kayaks, expanded polystyrene, lampshades |
| Sub 2 | 1 to under 2 | 300 | Fiberglass insulation batts, assembled wicker furniture, empty plastic tanks |
| Sub 3 | 2 to under 4 | 250 | Mattresses, HVAC spiral ductwork, upholstered seating |
| Sub 4 | 4 to under 6 | 175 | Assembled office cabinets, medical carts, refrigeration shells |
| Sub 5 | 6 to under 8 | 125 | Crated small pumps, vending machines, range hoods |
| Sub 6 | 8 to under 10 | 100 | Wine and beverage cases, auto body panels, boxed electronics |
| Sub 7 | 10 to under 12 | 92.5 | Commercial kitchen appliances, crated motors, boxed hardware |
| Sub 8 | 12 to under 15 | 85 | Machine parts, boxed tools, compressors, transmissions |
| Sub 9 | 15 to under 22.5 | 70 | Palletized canned goods, machinery components, cable reels |
| Sub 10 | 22.5 to under 30 | 65 | Bottled beverages, ceramic tile, boxed fasteners, dry chemicals |
| Sub 11New | 30 to under 35 | 60 | Sheet steel, bagged cement and mortar, lead-acid batteries |
| Sub 12New | 35 to under 50 | 55 | Bricks, hardwood flooring bundles, bar stock, brass fittings |
| Sub 13New | 50 or more | 50 | Steel coils, castings, bulk fasteners in kegs, granite slabs |
NMFC 13-subprovision density scale (NMFTA Docket 2025-1). Density = total weight including pallet ÷ total cubic feet. Commodity-specific NMFC items can still override density for some articles.
Two practical consequences. First, a load at 3.4 PCF (Class 250) whose imputed density falls to 1.97 PCF crosses into Class 300 before any cubic rule is applied. Second, the synthetic weight is often two to three times the scale weight, so even at Class 125 it out-prices the real weight at Class 250. The 13-tier density chart explains each subprovision.
Worked example: six non-stackable skids against eight carriers
Six 48×40 skids of light fixtures, each 56 in tall and 210 lbs including the pallet, marked do not stack. Shipped 1,000 miles.
| Measure | Calculation | Result |
|---|---|---|
| Actual cube per skid | 48 × 40 × 56 ÷ 1,728 | 62.2 cu ft |
| Actual cube, 6 skids | 62.22 × 6 | 373.3 cu ft |
| Imputed cube per skid | 48 × 40 × 96 ÷ 1,728 | 106.7 cu ft |
| Imputed cube, 6 skids | 106.67 × 6 | 640.0 cu ft |
| Phantom cube | 640.0 − 373.3 | 266.7 cu ft |
| Total weight | 210 × 6 | 1,260 lbs |
| Actual density | 1,260 ÷ 373.3 | 3.38 PCF (Class 250) |
| Imputed density | 1,260 ÷ 640.0 | 1.97 PCF (Class 300) |
| Linear feet | 3 rows of 2 across × 48 in ÷ 12 | 12 LF |
| Synthetic weight at 6 PCF | 640.0 × 6 | 3,840 lbs |
Now run that one load through each carrier's published triggers:
| Carrier | 350 cu ft / 3 PCF tier | 750 cu ft / 6 PCF tier | Linear foot rule | Outcome |
|---|---|---|---|---|
| Old Dominion | Not published | 640 < 750, clear | 12 < 15 LF, clear | Rates on scale weight |
| XPO | 640 ≥ 350 at 1.97 PCF, fires | Clear | 12 ≥ 12 LF, fires | Re-rated |
| Saia | Fires | Clear | Fires | Re-rated |
| FedEx Freight | Not published | Clear | Fires at 12 LF | Re-rated on linear feet |
| ABF Freight | Fires | Clear | Fires | Re-rated |
| Estes | Fires | Clear | Fires | Re-rated |
| R+L Carriers | Not published | Clear | Fires at 12 LF | Re-rated on linear feet |
| TForce Freight | Not published | Clear | Check UPGF 102 | Depends on the issue in force |
Indicative engine figures for this lane: about $583 rated cleanly at Class 250, about $1,219 once re-rated at the synthetic weight with a restricted discount and an inspection fee, about $882 as a spot volume LTL quote and about $1,033 on a direct partial truckload. On Old Dominion the clean rate holds and LTL is the cheapest option. On every carrier where a rule fires, volume LTL or partial truckload is cheaper than the re-bill. These are planning numbers, not quotes.
How a cubic re-bill reaches your desk
Most cubic capacity charges are not quoted. They arrive after delivery as a corrected invoice, usually with a weight and inspection (W&I) certificate attached. The sequence is the same at every national carrier:
- Dimensioner scan. The skids pass under an overhead laser or camera dimensioner at the origin or first break terminal. It records length, width, height and a photo.
- Stackability call. A dock supervisor or the system flags units that are labelled do not stack, have an irregular top, or exceed the carrier's height line. Those are re-measured at 96 in.
- Rule check. Billing compares the tariff cube, density and linear feet with the item thresholds.
- Re-rate. The invoice is rebuilt on synthetic weight, linear feet or the cubic minimum, often at a reduced discount, plus an inspection or correction fee.
Before you dispute, ask for the W&I certificate and dimensioner photos, compare them with the dimensions on your bill of lading, and read the item that was applied in the issue of the rules tariff that was in force on the ship date. Carriers reissue their rules tariffs, sometimes several times a year, and the current issue governs, not the one you saved last spring. Our W&I dispute guide walks through the paperwork.
Picking the mode before a rule fires
The cheapest fix for a cubic rule is to keep the load out of class-rated LTL when the numbers say it will fire. The thresholds below are the ones the engine uses for its green, amber and red badges.
| Load profile (tariff cube) | Typical result | Book it as |
|---|---|---|
| Under 350 cu ft, any density, under 12 LF | Rates on scale weight | Standard class-rated LTL |
| 350–749 cu ft at 3 PCF or more, under 12 LF | Usually clean | Standard LTL or spot volume LTL |
| 350–749 cu ft under 3 PCF | Tier 1 rule at XPO, Saia, ABF, Estes | Spot volume LTL or a carrier without the 350 tier |
| 750 cu ft or more under 6 PCF | Tier 2 rule at every national carrier | Direct partial truckload |
| 12 LF or more, any density | Linear foot rule at most carriers | Spot volume LTL or partial truckload |
Two habits remove most surprises. Measure each unit at its tallest point, including the pallet, and declare stackability honestly on the bill of lading. Then run the load through the linear foot calculator before you tender. If the badge is amber or red, send the dimensions to rates@cubictransport.com and we will price volume LTL and partial truckload side by side.
