The 13-Sub Density Structure
In North American Less-Than-Truckload (LTL) shipping, freight class ratings determine base transportation rates. Historically derived from commodity lookups, modern classification increasingly relies on density (pounds per cubic foot, or PCF). Below is the standard 13-sub full-scale density structure published by the NMFTA for density-based freight.
| Density Band (lb/ft³) | Freight Class | Typical Commodity Profile |
|---|---|---|
| Less than 1 | Class 400 | Extremely low density (ping pong balls, light foam, hollow plastics) |
| 1 to <2 | Class 300 | Very bulky cargo (lampshades, empty boxes, unwrapped insulation) |
| 2 to <4 | Class 250 | Bulky consumer goods (mattresses, hollow furniture) |
| 4 to <6 | Class 175 | Low-density boxed goods (light clothing, assembled cabinetry) |
| 6 to <8 | Class 125 | Medium-low density (small appliances, cookware, sporting goods) |
| 8 to <10 | Class 100 | Standard general merchandise (packaged consumer electronics) |
| 10 to <12 | Class 92.5 | Dense packaged goods (books, paper goods, bottled beverages) |
| 12 to <15 | Class 85 | Packaged non-perishables (canned foods, bulk dry goods) |
| 15 to <22.5 | Class 70 | Dense hardware (auto parts, hand tools, plumbing fixtures) |
| 22.5 to <30 | Class 65 | Heavy components (dense machinery parts, fasteners) |
| 30 to <35 | Class 60 | Industrial materials (steel bars, heavy hardware) |
| 35 to <50 | Class 55 | Very dense commodities (bricks, mortar, bulk hardware) |
| 50 or more | Class 50 | Extremely dense cargo (solid steel ingots, lead, cast iron) |
Boundary Handling & Exact Break Rules
Each density band is defined with a closed lower bound and an open upper bound. For example, a shipment with a calculated density of exactly 10.00 lb/ft³ is classified as Class 92.5 (10 to <12 PCF), not Class 100. Similarly, 15.00 lb/ft³ lands in Class 70. Precision in calculation is critical: a fraction of an inch or pound can push a shipment across a class boundary, causing significant rate changes on your freight bill.
Planning Caveat: Density vs Commodity Provisions
While density is the primary quantifiable metric, official National Motor Freight Classification (NMFC) tariffs also consider handling, stowability, and liability (susceptibility to theft or damage). Items with specific NMFC item numbers may have fixed classes regardless of density. Always confirm with your carrier or third-party logistics partner.