Freight class for LTL (less-than-truckload) shipments is determined by a combination of four factors: density, handling, stowability, and liability. The National Motor Freight Traffic Association (NMFTA) assigns each commodity an NMFC code tied to one of 18 freight classes, ranging from class 50 (easiest and cheapest to ship) to class 500 (most difficult and expensive). Getting this classification right on your bill of lading matters, because carriers will reclassify and rebill you if the declared class doesn’t match the actual shipment.
The Four Factors That Set Your Class
Every NMFC classification reflects how transportable a shipment is, based on four characteristics evaluated together.
Density is the most influential factor for most shipments. It measures how heavy a shipment is relative to the space it occupies, expressed in pounds per cubic foot. A compact, heavy pallet of metal parts has high density and earns a low (cheaper) freight class. A large, lightweight shipment of foam cushions has low density and lands in a higher, more expensive class.
Handling considers how much special care or equipment the shipment requires. Freight that can be loaded with a standard forklift and stacked normally is easy to handle. Items that are fragile, oddly shaped, or hazardous need extra attention and push the class higher.
Stowability refers to how well the freight fits alongside other shipments in a trailer. LTL carriers consolidate multiple shippers’ freight on one truck, so anything that can’t be stacked, must be kept away from certain materials, or takes up disproportionate floor space is harder to stow. Irregularly shaped items or goods with regulatory restrictions on how they’re loaded score poorly here.
Liability accounts for the risk of damage, theft, or spoilage during transit. Perishable goods, high-value electronics, and hazardous materials carry more liability for the carrier. Higher risk means a higher freight class.
For many everyday commodities, density alone drives the classification. But for items with unusual handling needs, hazardous properties, or high value, those other three factors can bump the class well above what density alone would suggest.
How to Calculate Density
Density is the one factor you can measure yourself before shipping. The formula is straightforward, but precision matters because carriers will verify your numbers.
Start by measuring the length, width, and height of your shipment in inches. Measure the extreme dimensions, meaning the widest, longest, and tallest points including all packaging, pallets, and any overhang. A box sitting on a pallet? Measure the full footprint of the pallet and the total height from the pallet’s bottom to the top of the box.
Next, convert those measurements into cubic feet:
- Length × Width × Height ÷ 1,728 = cubic feet
The 1,728 divisor converts cubic inches to cubic feet (12 × 12 × 12). Then divide the total shipment weight in pounds by the cubic feet:
- Total weight (lbs) ÷ cubic feet = density (lbs per cubic foot)
For example, a shipment measuring 48 × 40 × 36 inches on a pallet weighing 425 pounds total works out like this: 48 × 40 × 36 = 69,120 cubic inches. Divide by 1,728 to get 40 cubic feet. Then 425 ÷ 40 = 10.6 pounds per cubic foot. That density figure is what you’ll use to look up the appropriate freight class for your commodity.
If you’re shipping multiple pieces on one bill of lading, calculate the density for each piece separately when they’re different commodities, or calculate a combined density for identical items by adding up total weight and total cubic feet.
Looking Up Your NMFC Code and Class
Once you know your product type and its density, you need to find the correct NMFC item number. The NMFTA maintains a database called ClassIT that maps thousands of commodities to specific NMFC codes. Each code has rules that define which freight class applies, often with density breakpoints that assign different classes depending on how dense your particular shipment is.
For instance, a single NMFC item number for plastic parts might assign class 70 if the density is above 15 pounds per cubic foot, class 85 if it falls between 12 and 15, and class 92.5 if it drops below 12. The commodity description in the NMFC determines which density thresholds apply to your product.
Access to the full NMFC database requires a subscription through NMFTA. However, most freight brokers, third-party logistics providers, and carrier websites offer classification tools where you enter your commodity description, weight, and dimensions to get a class estimate. Many LTL carriers also publish density-based class charts as a general reference, though the official NMFC classification always takes precedence.
When searching for your NMFC code, be specific about what you’re shipping. “Machine parts” is too broad. The classification system distinguishes between cast iron machine parts, plastic machine parts, and electronic machine components because each has different handling, liability, and stowability profiles.
Why Accurate Classification Saves You Money
Carriers increasingly use automated dimensioning equipment at their terminals to verify that what’s on the bill of lading matches the actual freight. These dimensionalizers scan shipments for length, width, height, and sometimes weight as they move through the dock. If the measured dimensions or weight produce a different freight class than what you declared, the carrier will reclassify your shipment and send you a revised, higher invoice.
Reclassification charges can be significant. You pay the difference between your declared class rate and the correct class rate, and some carriers add inspection or adjustment fees on top. Disputing a reclassification is possible, but carriers no longer accept product spec sheets as proof of weight. You need certified scale tickets from regularly calibrated, state-certified scales to challenge a reweigh.
A few practical steps reduce your risk. Weigh every shipment on a calibrated scale rather than relying on product specs or estimates. Measure dimensions after the freight is packaged and palletized, not before. Photograph how the freight is loaded, especially for oversized pallets, so you have documentation of the actual dimensions if a carrier questions them. And double-check that the NMFC code on your bill of lading matches the specific product you’re shipping, not just a similar-sounding commodity.
Recent Changes to the Classification System
The NMFTA is in the middle of a significant overhaul of the NMFC. Phase 1 of these changes took effect on July 19, 2025, fundamentally shifting how certain freight is classified, rated, and billed. Additional reclassifications and rule updates are expected in future phases throughout 2025 and beyond, affecting a broader range of commodities and shipment types.
The practical impact is that NMFC codes and class assignments you’ve used for years may no longer be accurate. The NMFTA publishes a Disposition Bulletin before each round of changes that lists every approved modification. If you ship regularly, check with your carrier or logistics provider after each update to confirm your commodity classifications are still correct. Shipping on an outdated NMFC code is one of the fastest ways to trigger a reclassification charge.
The 18 Freight Classes at a Glance
Freight classes run from 50 to 500 in specific increments: 50, 55, 60, 65, 70, 77.5, 85, 92.5, 100, 110, 125, 150, 175, 200, 250, 300, 400, and 500. Lower classes correspond to freight that is dense, durable, easy to handle, and low risk. Higher classes correspond to freight that is light for its size, fragile, awkward to move, or high in value.
As a rough guide, class 50 freight typically runs above 50 pounds per cubic foot (think bricks, sand, or nuts and bolts). Class 500 freight can be as light as one pound per cubic foot or less (like ping pong balls or bags of gold dust with extreme liability). Most general commercial freight falls somewhere between class 70 and class 150.
Your shipping rate per hundred pounds (called the hundredweight rate) increases as freight class goes up. The jump between adjacent classes isn’t always proportional, so even a one-class miscalculation can meaningfully change your shipping cost, especially on heavier shipments.