Freight Class & NMFC Codes Explained: A Shipper's Complete Guide

Freight class is the single most important, and most misunderstood, number in LTL shipping. Get it right, and your invoice matches your quote. Get it wrong, and the carrier will reclassify your freight in transit and bill you the difference plus a penalty. Here's everything you need to know.

What freight class actually is

Freight class is a number between 50 and 500 that the National Motor Freight Classification (NMFC) system assigns to every type of commodity. The class reflects how difficult and risky a commodity is to ship, based on density, value, handling, and liability. Class 50 is the cheapest to ship (dense, durable freight that loads easily). Class 500 is the most expensive (light, fragile, awkward freight that takes up trailer space without weight).

LTL carriers use freight class to determine how much trailer capacity your shipment effectively consumes. A class-50 load and a class-500 load might weigh the same on the scale, but the class-500 load is taking up more of the carrier's revenue-generating capacity per pound, so it's priced higher per hundredweight (CWT).

The four factors that determine freight class

The NMFC assigns class based on four factors. For most commercial freight, density alone drives the class. The other factors only become relevant for unusual commodities.

1. Density (the dominant factor)

Density is pounds per cubic foot. Calculate it by:

1. Measuring the length, width, and height of your shipment in inches (including pallets, crates, and any overhang).
2. Multiplying L × W × H to get total cubic inches.
3. Dividing by 1,728 to convert to cubic feet.
4. Dividing the shipment's total weight (in pounds) by the cubic feet.

The result is your density, and the density alone determines class on most NMFC items.

2. Stowability

Whether the freight can be stacked or loaded next to other freight without damage or hazard. Long, awkwardly shaped, or hazmat freight has worse stowability and gets a higher class.

3. Handling

Whether the freight requires special handling, fragile, oversized, requires team lift, requires special equipment to load or unload. More handling = higher class.

4. Liability

Risk of theft, damage, or damage to surrounding freight. High-value or hazardous commodities get higher classes regardless of density.

The density-to-class chart

For most freight, this single chart tells you your class:

A worked example

What NMFC codes are

Beyond the class number, every commodity has a specific NMFC item number, a 6-digit code that identifies what you're shipping. NMFC item 156600, for example, refers to "Furniture." Item 65500 is "Iron or Steel Articles." The full NMFC catalog has tens of thousands of items and is maintained by the National Motor Freight Traffic Association (NMFTA).

Most LTL carriers require both the class and the NMFC item number on the BOL. The NMFC number tells the carrier exactly what they're hauling; the class tells them how to price it.

How to avoid reclassification fees

Reclassification (sometimes called "reclass" or "reweigh and inspection") is when the carrier audits your freight in transit, measures and weighs it themselves, and determines that the class or weight you declared was wrong. They'll reclassify the shipment, bill the difference, and add a $50 to $150 reclassification fee.

This happens to a huge percentage of LTL shipments. Here's how to avoid it:

• Measure your freight accurately. Include pallets, overhang, and packaging. "Eyeballing it" is the single biggest cause of reclassification.
• Weigh every shipment. Don't go off product spec sheets, actual freight often weighs more than the catalog number due to packaging, banding, and pallet weight.
• Use the correct NMFC item. Generic "general merchandise" classifications are red flags that invite scrutiny.
• Don't round down. If your density calculation puts you right on a class boundary, the carrier will round up, you should too.
• Account for empty space. Two pallets that are mostly empty space have low density. Density is based on the full dimensional footprint, not just the volume of the items themselves.

Density-based vs class-based pricing

Most major LTL carriers now offer density-based pricing (sometimes called "dynamic pricing") as an alternative to traditional class. Instead of looking up your class on a tariff, the carrier just bills based on actual density and dimensions. The advantage: no reclassification fees, because there's nothing to misclassify. The disadvantage: you need accurate dimensions upfront, and you lose some of the predictability of class-based pricing.

Density-based pricing is the direction the industry is moving, but it's still in transition. Most shippers should understand both, your broker will tell you which one applies on your lane.

The bottom line

Freight class is a calculation, not a guess. Measure your freight accurately, weigh every shipment, and use the right NMFC item number. The most expensive class is always the one the carrier corrects in transit, because then you're paying not just for the higher class but for the reclassification fee on top of it.

If you're shipping LTL regularly with consistent product, ask your broker to help you confirm the right class for your typical shipment specs. Getting it right once means every future quote holds, and your invoice matches what you were quoted, every time.

Frequently asked questions