What Is Freight Class? The NMFC System Explained

If you ship less-than-truckload (LTL) freight, no single number affects your price more than freight class. Get it right and your rates are predictable. Get it wrong and you'll face reclassification charges, disputes, and budget surprises. Here's how the system actually works.

What freight class is

Freight class is a standardized number — one of 18 classes from 50 to 500 — that groups commodities by how difficult and costly they are to transport. Lower classes (like 50 or 55) are dense, durable, easy-to-handle goods that cost less to ship. Higher classes (like 300 or 500) are light, bulky, fragile, or valuable goods that cost more.

The system is published by the National Motor Freight Traffic Association (NMFTA) in the National Motor Freight Classification (NMFC). Nearly every LTL carrier in North America uses it as the common language for pricing.

The four factors that determine class

• Density — weight per cubic foot. This is the biggest driver for most freight. Denser freight = lower class = cheaper.
• Stowability — how easily it fits with other freight. Odd shapes, overlength, or hazardous items are harder to stow.
• Handling — how much care it takes to load, unload, and move.
• Liability — the value, fragility, and theft/damage risk of the goods.

Density-based vs. fixed-class items

This is where shippers get tripped up. Some NMFC items are density-based: the class changes with how dense the shipment is, according to a published density scale. Others are assigned a fixed class regardless of density, because the commodity itself carries a specific handling or liability profile.

So you can't always calculate your way to a class from density alone — you need to find the actual NMFC item number for your commodity first, then apply its rule.

How to find your freight class

1. Identify the commodity's NMFC item number. The authoritative source is NMFTA's ClassIT+ database.
2. Check whether the item is density-based or fixed. If fixed, you're done — use that class.
3. If density-based, calculate your density (total weight ÷ total cubic feet) and read the class off the item's density scale.

Why getting it right matters

Carriers inspect freight. If your bill of lading lists a lower class than the freight actually warrants — usually because the density was overstated or the wrong item was used — the carrier reweighs or re-measures it, reclassifies it, and sends a balance-due adjustment. Those adjustments are one of the most common (and avoidable) sources of unexpected LTL cost.