How to Calculate Freight Class: A Complete Step-by-Step Guide

What You'll Need to Calculate Freight Class by Hand

Before you start, gather these supplies and tools:

• Measuring tape (or ruler) to measure length, width, and height of each package in inches or centimeters
• Scale (bathroom or shipping scale) to weigh each item in pounds or kilograms
• Calculator (or use our Freight Class Calculator for quick results)
• Paper and pen to record dimensions and weights
• NMFC class chart (see the table in our Freight Class Ranges 50-500 guide)

Step-by-Step Guide to Calculate Freight Class Manually

Follow these steps to determine your shipment's NMFC class. The key formula is:

Density (lbs/cu ft) = Total Weight (lbs) ÷ Total Volume (cubic feet)

For a deeper dive into the formula, see our Freight Class Density Formula page.

1. Measure each package's dimensions. Use the same unit (inches or centimeters). Measure length, width, and height of the packaged item, not just the product itself. Include any packaging materials.
2. Calculate the volume of one package. Multiply length × width × height. If using inches, divide by 1,728 to convert to cubic feet. If using centimeters, divide by 28,316.8 to get cubic feet.
3. Multiply volume by the number of identical packages. If you have multiple items of the same size, total volume = volume per package × number of items.
4. Weigh the total shipment. Weigh all items together on a scale. Record the total weight in pounds (or convert from kilograms by multiplying by 2.20462).
5. Calculate density. Divide total weight by total volume. The result is pounds per cubic foot. If density is below 1, double-check your measurements — very low density is unusual.
6. Find the corresponding freight class. Use an NMFC density table. For example, if density is 12.5 lbs/cu ft, look up the range 12–13.5, which maps to class 85. Our What Is Freight Class? page includes a complete table.
7. Verify stowability and handling. In rare cases, items that are extremely heavy, fragile, or oddly shaped may be bumped to a higher class (e.g., class 250 or 300). Most shipments, however, are classified purely by density.

Worked Example 1: Medium Box of Books

You're shipping a single box of books. The box measures 18 inches long, 12 inches wide, and 10 inches high. It weighs 25 pounds.

• Volume in cubic feet = (18 × 12 × 10) ÷ 1,728 = 2,160 ÷ 1,728 = 1.25 cu ft
• Weight = 25 lbs
• Density = 25 ÷ 1.25 = 20 lbs/cu ft

Looking at the NMFC table, a density of 20 falls between 15 and 22.5, which corresponds to class 70. So your books would be class 70.

Worked Example 2: Pallet of Light Garden Tools

You have a pallet containing 50 identical garden tool sets. Each set is packed in a box 24" × 18" × 12" and weighs 8 lbs. The pallet itself adds 30 lbs and has a volume of about 2 cubic feet (but we'll ignore pallet volume for simplicity — always include it if it's significant).

1. One box volume = (24 × 18 × 12) ÷ 1,728 = 5,184 ÷ 1,728 = 3 cu ft
2. Total volume = 3 cu ft × 50 = 150 cu ft
3. Total weight = (8 lbs × 50) + 30 lbs = 400 + 30 = 430 lbs
4. Density = 430 ÷ 150 = 2.867 lbs/cu ft

A density around 2.87 is very low. The NMFC table shows that for density below 1, class 500 applies, but between 2 and 3, it's usually class 500 as well (check the full table; density under 4 maps to class 400 or 500). In this case, typical class for such low density is 500. That means high shipping costs. Consider consolidating or repacking to increase density.

Common Pitfalls to Avoid

• Forgetting packaging volume. Always measure the outermost dimensions of the shipping package, not the product alone. Box flaps, padding, and pallet overhang add volume and lower density.
• Mixing units. Use all inches or all centimeters for volume, then convert consistently. Mixing feet and inches leads to errors.
• Ignoring pallet weight. For LTL shipments, the pallet's weight and volume count. Include them in your totals. See our guide on Freight Class for LTL Shipping.
• Using wrong density range. The NMFC table boundaries are precise (e.g., 12.0 to 13.5 is class 85, but 13.5 to 15 is class 77.5). Rounding can push you into the wrong class. Always use raw numbers without rounding until the final step.
• Not rechecking after repackaging. Changing box size or adding padding changes density. Recalculate every time you modify packaging.

When to Use the Calculator Instead

Manual calculation is great for understanding the process, but for speed and accuracy, use our Freight Class Calculator. It handles conversions, avoids mistakes, and gives instant results. Try it for your next shipment.