How to Calculate Freight Class
For most shipments, freight class comes down to density - how many pounds your freight weighs per cubic foot. Here is the formula, a worked example, and when density is not the final word.
The density formula
Volume (ft³) = (Length × Width × Height in inches) ÷ 1,728
Density (lbs/ft³) = Weight (lbs) ÷ Volume (ft³)
1,728 is the number of cubic inches in one cubic foot (12 × 12 × 12).
Worked example
A pallet of goods: 500 lbs, measuring 48 × 40 × 48 inches.
- Volume = (48 × 40 × 48) ÷ 1,728 = 53.3 ft³
- Density = 500 ÷ 53.3 = 9.4 lbs/ft³
- A density around 9–10 lbs/ft³ typically lands near class 100–125.
Want this done for you? The freight class calculator computes density and the estimated class as you type.
Density → class rule of thumb
| Density (lbs/ft³) | Typical class |
|---|---|
| 50+ | 50 |
| 30–35 | 55–60 |
| 15–22.5 | 65–70 |
| 10.5–15 | 77.5–85 |
| 7–10.5 | 92.5–110 |
| 5–7 | 125–175 |
| 2–5 | 200–300 |
| under 2 | 400–500 |
A rule of thumb based on the standard NMFC density brackets. The official NMFC listing for a commodity always takes precedence.
When density isn't the final answer
Many commodities have a fixed class in the NMFC regardless of density, and class also factors in stowability, handling, and liability. So density gives you an estimate - for the rated class, look the commodity up in the NMFC database.
Frequently asked questions
How do you calculate freight class?
Calculate density: divide the shipment weight in pounds by its volume in cubic feet (length × width × height in inches, divided by 1,728). Then match that density to a freight class - higher density gives a lower class. For commodities with a fixed NMFC class, look the item up instead of using density.
What is the freight class density formula?
Density (lbs/ft³) = weight in pounds ÷ (length × width × height in inches ÷ 1,728). 1,728 is the number of cubic inches in a cubic foot.
Does higher density mean a higher or lower freight class?
Higher density means a LOWER freight class and a lower shipping rate. Dense, compact freight is cheaper to ship than light, bulky freight.
Is freight class always based on density?
No. Many NMFC commodities have a fixed class regardless of density, and some are graded into density brackets. Density is the general rule of thumb, but the official NMFC listing is authoritative - look up the commodity to be sure.