How to Calculate Freight Class

1. Measure the biggest outside edges

   Length, width and height of the piece exactly as it will travel — box bulges, wrapping, and anything sticking out. If it rides on a pallet, the pallet is part of the piece: footprint and height both count.

2. Work out the volume

   Multiply the three measurements in inches and divide by 1,728 to get cubic feet.
   Volume (ft³) = L × W × H ÷ 1,728

3. Divide weight by volume

   That gives density in pounds per cubic foot (pcf) — the number the whole system runs on.
   Density (pcf) = weight (lb) ÷ volume (ft³)

4. Read the class off the chart

   Find your density in the freight class chart. The class beside it is your density-based freight class. Exactly on a line? The line belongs to the denser band — 10.00 pcf is 92.5, not 100.

A worked example

A crate measures 36 × 36 × 36 in and weighs 200 lb, packaging included.

• Volume: 36 × 36 × 36 ÷ 1,728 = 27.00 ft³
• Density: 200 ÷ 27.00 = 7.41 pcf
• On the chart, 7.41 pcf falls in the 6–8 band → Class 125

Try it yourself: run this crate in the calculator.

The pallet mistake that costs a class

Say your freight stacks 42 in high on a standard 48 × 40 in pallet, and the loaded piece weighs 500 lb. Measure just the freight and you get one answer; measure the way the carrier does — pallet included, 48 in high — and you get another:

Same freight, same weight — one class apart, because six inches of pallet height spread the same 500 lb over more cubic feet. Quote with the freight-only number and the carrier's re-measurement will move you to the higher class and re-rate the bill. Always measure the full outside of the piece as it ships.

What changed in 2025 — and the classes density no longer makes

On July 19, 2025 the density scale was expanded from 11 to 13 subprovisions (Docket 2025-1). Before that, the scale also produced Class 500 for very light freight, plus 200, 150, 110 and 77.5. Density no longer produces any of those. Today the full range from density is 400 (lightest) down to 50 (densest). If a density calculator or chart gives you 500, its density table is out of date — Class 500 no longer comes out of the density scale (a specific NMFC item can still carry it).

When density doesn't decide the class

Density is the rule for most everyday freight, but not all of it. Some products have a fixed class written into their NMFC item that applies whatever the density works out to, and a few goods are classed on other factors as well. A density calculator — this one included — gives you the density-based estimate. If your product has its own NMFC item, that item and your carrier's measurement have the final word.

Formulas use inches and pounds; the calculator also accepts feet, cm and kg. See the published test cases for boundary examples for every class.