How to Calculate Freight Class (Formula + Worked Examples)

Freight class is the number an LTL carrier uses to price a shipment. For most density-rated commodities in the US, you can calculate it in three steps: measure the handling unit, divide its weight by its cube, and match the result to the 2025 NMFC density scale.

That sounds simple. The mistakes usually happen before the math: measuring the freight instead of the pallet, using net weight instead of gross, or checking an old 18-class chart that still lists Class 110 as a density result.

This guide shows the full calculation with real numbers, the current scale, and the details that change the answer.

What freight class actually is

The National Motor Freight Classification (NMFC) assigns classes from 50 to 500. Lower classes are generally cheaper to move; higher classes are generally more expensive. The class reflects four transportation characteristics:

• Density — weight relative to the space the freight occupies.
• Handling — how difficult the freight is to move, load, or secure.
• Stowability — how well it fits into a trailer with other freight.
• Liability — risk of damage, theft, or claims.

Density is the most visible factor, and for many commodities it is the primary one. It is not the only one. A dense item that is fragile, hazardous, or awkward to handle can still carry a class that density alone would not predict.

That is why a calculator result is an estimate, not an official NMFC rating. The NMFC item description and the carrier’s tariff control the final class.

The density formula

Density is pounds per cubic foot (lb/ft³):

Density = gross weight (lb) ÷ volume (ft³)

For a box or a pallet, volume in cubic feet is:

Volume (ft³) = length (in) × width (in) × height (in) ÷ 1,728

The 1,728 comes from 12 × 12 × 12 — the number of cubic inches in a cubic foot.

For a cylinder, measure the diameter and the height. Freight calculators commonly cube the drum as a bounding box:

Cylinder volume (ft³) = diameter (in) × diameter (in) × height (in) ÷ 1,728

That is the space the drum occupies in a trailer, even though the drum itself holds less. It is a conservative way to estimate density.

A worked example

Take a standard GMA pallet: 48 × 40 inches, loaded to a total height of 48 inches, with a gross weight of 425 pounds.

Step 1 — volume.

48 × 40 × 48 = 92,160 in³
92,160 ÷ 1,728 = 53.33 ft³

Step 2 — density.

425 lb ÷ 53.33 ft³ = 7.97 lb/ft³

Step 3 — lookup. On the 2025 scale, 7.97 lb/ft³ falls in the 6-to-under-8 band. That is Class 125.

The next cheaper class is Class 100, which starts at 8 lb/ft³. At the same 53.33 ft³, you would need 8 × 53.33 = 426.7 pounds — about 1.7 more pounds. Or you could remove about 0.2 inches of height at the same weight. Small changes at a boundary can move the class.

That is why boundary insight matters more than a single number. A shipment at 7.97 is not “basically Class 100.” It is Class 125 until it crosses 8.0.

The 2025 NMFC density scale

Since July 19, 2025, most density-rated commodities use a single 13-tier scale from Class 50 to Class 400.

The NMFC still has 18 classes overall. Classes 77.5, 110, 150, 200, and 500 remain for commodity-specific items, but they are not outputs of the density scale. If a calculator returns Class 110 for a density lookup, it is using an old chart.

How to measure a pallet correctly

The measurement should describe the handling unit as tendered, not the product inside it.

• Length and width: measure the widest points, including cartons that overhang the pallet deck.
• Height: measure from the floor to the top of the highest point. Include the pallet deck. If the load is banded or wrapped, include the wrap and any top caps.
• Weight: use gross weight — freight, cartons, packaging, and pallet. A standard GMA wood pallet is often around 37 pounds; a Euro pallet is often around 55 pounds. Those pounds count.
• Quantity: if you have identical handling units, use one line and set the quantity. If the pallets differ, enter each size separately.
• Shape: for a drum or cylinder, use the diameter as both length and width. The calculator cubes it as a bounding box.

Do not measure a pallet at its nominal 48 × 40 if the freight overhangs. Do not use the height of the product before it was stacked. Do not weigh only the goods.

Common mistakes that change the class

Using net weight. The carrier weighs the handling unit. If you leave out the pallet and packaging, your density is too low and your class is too high.

Measuring the freight, not the pallet. A carton that is 24 × 18 × 12 on a 48 × 40 pallet still occupies the pallet’s footprint. Use the pallet dimensions.

Rounding down the height. A 48.5-inch load is not 48 inches. At the same weight, that half inch can push density below a boundary.

Mixing pallets on one line. Two pallets with different dimensions and weights should be separate lines. The combined density may look fine while one pallet is much lighter and rates higher on its own.

Forgetting the pallet weight. A 37-pound pallet on a 400-pound load is nearly 9% of the gross weight. On light freight, it can move the class.

Using an old chart. The 2025 scale does not return Class 110, 150, 200, 77.5, or 500 for density. Use the 13-tier table.

Assuming the lowest class wins. If a mixed shipment ships as separate handling units, a carrier may rate at the highest class. The combined density class assumes the units can be rated together.

When density is not enough

Density is one of four classification factors. Some commodities have NMFC item numbers with specific classes, subprovisions, or packaging rules that override a simple density lookup. Examples include:

• Hazardous materials and items with special handling requirements.
• High-value electronics, artwork, or fragile goods with liability surcharges.
• Oversized or irregular freight that does not stack or load cleanly.
• Commodities with a density subprovision that requires a specific package or minimum weight.

For those shipments, use the NMFC item and the carrier’s tariff. If you are unsure, ask the carrier to confirm the class before pickup. A written confirmation is cheaper than a reclass fee.

The bottom line

Calculate density from the handling unit as tendered. Match it to the 2025 13-tier scale. Treat the result as a strong estimate, then check the NMFC item and the carrier’s rules for the commodity you are shipping.

If you want to see the full math for your own shipment — including per-pallet classes and the weight or height needed to reach the next tier — use the Freight Class & Density Calculator. If you need the full table, the 2025 freight class chart is printable and includes the 48 × 40 pallet weight equivalents.