Freight Class Basics: How Classification Impacts Your Costs

What is a freight class and how does it affect pricing? This guide breaks down the NMFTA classification system, walks you through how to calculate freight density, and shows you how to avoid the reclass charges and billing disputes that come from getting it wrong. Whether you manage LTL shipping in-house or work with a transportation management partner, understanding freight class is one of the most direct ways to control your costs.

What Is Freight Class?

Freight class is a standardized category system that carriers use to price less-than-truckload (LTL) shipments based on the type of goods being shipped. The National Motor Freight Traffic Association (NMFTA) created this system so that every carrier prices the same type of commodity in a consistent way. There are eighteen classes, ranging from class 50 (the cheapest to ship) to class 500 (the most expensive).

If you ship LTL freight, your freight class is one of the biggest factors on your invoice. Getting it wrong leads to reclass charges, billing disputes, and strained carrier relationships. Getting it right means predictable costs and smoother operations.

In this post, we will walk through how freight class works, how to calculate it, and how to avoid the most common classification mistakes that drive up LTL shipping costs.

How Freight Class Affects LTL Shipping Costs

Every LTL carrier uses freight class as a starting point for calculating your rate. A lower class (like class 50) means your freight is dense, easy to handle, and cheap to move. A higher class (like class 300) means your freight takes up more space relative to its weight, requires more care, or carries more risk.

When you get a freight bill that is higher than expected, how do you figure out what went wrong? In many cases, the answer comes back to classification. Here is how it plays out:

• Base rate calculation: Your freight class plugs directly into the carrier's rate table. A higher class means a higher per-hundredweight rate before any discounts are applied.
• Reclass charges: If the carrier inspects your shipment at the terminal and determines the class on your bill of lading is wrong, they will reclassify it and bill you the difference, plus a fee.
• Reweigh and inspection fees: Carriers routinely use freight dimensioners to audit shipments. If your documented weight or class does not match what they find, you will pay for the inspection on top of the corrected rate.

The bottom line is simple. Accurate classification protects your budget. Inaccurate classification creates surprises.

The 4 Factors That Determine Freight Class

The NMFTA evaluates every commodity based on four characteristics. Understanding these helps you classify your shipments correctly before they leave the dock.

Density

Density is the most important factor. It measures how much your shipment weighs relative to the space it occupies, expressed in pounds per cubic foot. Heavier, more compact freight gets a lower class and a lower rate. Lighter, bulkier freight gets a higher class.

Think of it this way. A pallet of steel bolts is very dense and easy for a carrier to fit into a trailer. A pallet of lampshades weighs almost nothing but takes up the same amount of space. The lampshades will cost significantly more to ship per pound.

Stowability

Stowability describes how easily your freight fits alongside other shipments in a trailer. Carriers need to pack trailers tightly to stay profitable, so anything that wastes space increases your class.

Common stowability issues include:

• Irregularly shaped items that cannot sit flush against other pallets
• Hazardous materials that require physical separation from certain goods
• Freight that cannot be stacked, forcing empty space above it

Handling

Handling covers the physical effort required to load and unload your freight. Standard palletized goods that move easily with a forklift get favorable ratings. Fragile items, temperature-sensitive products, or shipments requiring special equipment push the class higher.

Good packaging can sometimes improve your handling rating. If you can make your freight easier for a dock worker to move safely, you may reduce your classification.

Liability

Liability measures the financial risk a carrier takes on when hauling your goods. Products that are high in value, prone to theft, or easily damaged carry more risk. Perishable goods that can spoil during transit also increase liability.

Carriers look at damage susceptibility and historical claims data when evaluating this factor. If your product has a track record of generating freight claims, expect a higher class.

How to Calculate Freight Class

Calculating your freight class is a straightforward process, but precision matters. A small measurement error can push your shipment into a different class and change your costs. Here is how to do it step by step.

Measure dimensions and weight

Measure your shipment exactly as it will travel, including the pallet, shrink wrap, and any protective packaging. Carriers measure the outermost edges, so you need to do the same.

• Record length, width, and height in inches at the longest points
• Weigh the fully packaged shipment on a calibrated scale
• Always include the pallet in your measurements

Calculate freight density

Multiply your length, width, and height (in inches) to get total cubic inches. Divide that number by 1,728 to convert to cubic feet. Then divide the total weight by the cubic feet. The result is your freight density in pounds per cubic foot. Carriers may also apply the cubic capacity rule when lightweight shipments take up excessive trailer space relative to their weight.

You can also use a freight density calculator online to speed this up. Either way, this number is the key input for determining your class.

Match density to the correct NMFC code

Once you know your density, look up your commodity in the NMFC directory. Find the item number that matches your product description, then identify the correct sub-number based on your density range. The sub-number determines your final freight class.

Do not guess or rely on outdated references. NMFC codes are updated regularly, and using the wrong one is one of the fastest ways to trigger a carrier dispute.

Freight Class Chart

This freight class chart gives you a general reference for how density ranges map to each of the eighteen classes. Use it as a starting point, but always verify your classification against the official NMFC directory.

Keep in mind that commodity type matters just as much as density. Two products with the same density can have different NMFC codes and different classes based on handling, stowability, and liability factors.

NMFC Codes and Why They Matter

NMFC codes and freight class are related but not the same thing. An NMFC code is the specific item number assigned to a particular commodity. The freight class (50 through 500) is the pricing tier that the code points to.

Why does this distinction matter? Because your bill of lading needs both. The NMFC code tells the carrier exactly what you are shipping. The class tells them how to price it. If the code is wrong or missing, the carrier will inspect the freight and assign their own classification, almost always at a higher cost to you.

Here is how the system is structured:

• Item number: The primary NMFC code for a broad commodity category
• Sub-number: A more specific variation based on packaging type or density range
• Class assignment: The freight class that corresponds to your exact item and sub-number combination

Dimensional Weight vs. Freight Density

If you ship both parcel and LTL freight, it is easy to confuse dimensional weight pricing with freight density. They solve a similar problem (accounting for lightweight, bulky shipments) but they work differently and apply to different modes.

Applying a parcel DIM factor to an LTL quote will give you the wrong answer. Make sure your team knows which calculation to use for each shipping mode.

Common Freight Classification Mistakes

Even experienced shipping teams make classification errors. These mistakes are preventable, but they require attention to detail and consistent processes.

• Inaccurate dimensions: Estimating pallet size instead of measuring it is the most common cause of reclass charges. Always measure freight as it sits on the dock, ready to ship.
• Wrong NMFC code: Using an outdated code or guessing the item number leads to billing disputes. Verify the correct code for every new product before the first shipment moves.
• Ignoring packaging changes: When your product team changes box sizes or pallet configurations, the density changes. A new package design can easily push your freight into a higher class.
• Assuming FAK covers everything: Freight-all-kinds agreements simplify pricing, but they have strict density and commodity limitations. Shipping outside those boundaries will trigger penalty charges.

How the Right Logistics Partner Helps You Avoid Classification Errors

Managing freight classification manually across dozens or hundreds of SKUs is time-consuming and error-prone. This is where working with an experienced logistics partner makes a real difference.

Redwood's Modern 4PL approach connects your transportation management processes to accurate, up-to-date classification data. Instead of relying on spreadsheets or outdated tariff books, you get automated rating and routing that catches errors before shipments leave the dock. This means fewer reclass charges, fewer carrier disputes, and more predictable LTL costs.

An open ecosystem model also gives you the flexibility to integrate classification tools with your existing systems, rather than forcing you onto a single platform. The result is cleaner data, better carrier compliance, and a freight audit process that actually works.

Final Thoughts

Freight class is not just a technical detail. It is one of the most direct levers you have for controlling your LTL shipping costs. When you understand how classification works, measure your freight accurately, and use the correct NMFC codes, you eliminate the billing surprises that eat into your margins.

If classification errors are a recurring problem, or if your team is spending too much time managing this process manually, it may be time to bring in a partner who can help you get it right. Contact Redwood to start the conversation.

Freight Class FAQ

What is the difference between freight class and NMFC code?

An NMFC code is the specific item number assigned to a commodity based on its characteristics. The freight class is the broader pricing category, ranging from 50 to 500, that the NMFC code determines.

Can freight class change if you update your packaging?

Yes. If new packaging changes the overall dimensions or density of your shipment, the freight class will likely change. You should recalculate density every time you alter your box size or pallet configuration.

What happens if the wrong freight class is listed on a bill of lading?

The carrier will flag the discrepancy during a terminal inspection and reclassify the shipment. This results in additional charges on your invoice, potential delivery delays, and a billing dispute you will need to resolve.

How do you find the correct NMFC code for a specific product?

You can use the ClassIT tool provided by the NMFTA, or you can work with your logistics provider to identify the correct item number based on your exact commodity description and packaging.