How the calculators work — and where they stop

Principles

The calculators are built around three rules. First, use the handling unit as tendered, not the product inside it. Second, show the formula and the boundary math, not just a class or a floor length. Third, state the limits so an estimate is not mistaken for an official NMFC classification or a carrier load plan.

There are no sponsored results, no carrier rankings, and no hidden affiliate weighting in the calculation. The same inputs produce the same output for every visitor.

The formula

Density is total gross weight divided by total cube:

density (lb/ft³) = gross weight (lb) ÷ volume (ft³)

For a rectangular handling unit, volume in cubic feet is:

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

The divisor 1,728 is 12³, the number of cubic inches in a cubic foot. A cylinder is cubed as its bounding box: diameter × diameter × height ÷ 1,728. That measures the space the drum occupies in a trailer, not its liquid capacity.

A worked example

A 48 × 40 × 48 in pallet at 425 lb gross:

48 × 40 × 48 = 92,160 in³
92,160 ÷ 1,728 = 53.33 ft³
425 ÷ 53.33 = 7.97 lb/ft³
7.97 lb/ft³ → Class 125

Class 100 starts at 8.0 lb/ft³. At the same 53.33 ft³, that requires 426.7 lb — about 1.7 lb more. The calculator reports that gap so a near-boundary shipment is visible.

The density scale

The calculator uses the 13-tier scale effective July 19, 2025. The lower bound of each band is inclusive: exactly 8.0 lb/ft³ is Class 100, and 7.999 is Class 125.

The NMFC still has 18 classes. Classes 77.5, 110, 150, 200, and 500 remain for commodity-specific items and are never returned by a density lookup here. See the chart page for the full legacy reference.

Units and conversion

Internally, every dimension is stored in inches and every weight in pounds. Changing the display unit converts the input; it does not change the shipment.

• Inches to feet: divide by 12.
• Centimeters to inches: divide by 2.54.
• Kilograms to pounds: multiply by 2.2046226218.
• Pounds per cubic foot to kilograms per cubic meter: multiply by 16.01846337396.

Displayed numbers are rounded for readability. Calculations use the unrounded converted values, so a displayed 7.97 lb/ft³ is still evaluated at full precision against the 8.0 boundary.

Pallets, quantity, and handling units

There are two measurement modes. Full handling unit means the dimensions and weight you enter already include the pallet. Freight + pallet adds the pallet footprint, deck height, and pallet weight to the freight.

The GMA preset is 48 × 40 × 5.5 in and 37 lb. The Euro preset is 47.24 × 31.5 × 5.7 in and 55 lb. These are common nominal values, not a guarantee for a specific pallet. Weigh and measure your own if the result is near a boundary.

Quantity multiplies both the cube and the weight, so density is unchanged by quantity. Quantity does change the total cube, total weight, and the weight or volume needed for a target class.

Per-line versus combined class

Each valid line gets its own density and class. The shipment also gets a combined class based on total weight and total cube. These can differ.

The combined class assumes the handling units can be rated together by total density. If they ship as separate units, a carrier may rate each line or apply the highest line class. The calculator flags a mixed-class shipment and shows the highest line class so the assumption is visible.

Boundary and target math

For the next cheaper class, the required weight at the current cube is:

required weight = next band minimum density × current total cube

Or, to keep the current weight and shrink the cube:

required cube = current total weight ÷ next band minimum density

For a single-line shipment, the required height is derived from the required cube and the line’s footprint. These are planning numbers. They do not account for how the freight is stacked, whether the height is physically achievable, or the carrier’s handling rules.

Linear feet and trailer floor space

The linear feet calculator uses the same handling-unit dimensions as the class calculator, but the output is floor length rather than density. For each line, the side running down the trailer is the row depth. The side across the trailer sets how many units share a row:

units across = floor(usable trailer width ÷ side across)
rows = ceil(floor positions ÷ units across)
floor length (in) = rows × row depth + row gaps
linear feet = floor length ÷ 12

Floor positions are the quantity divided by the effective stack, rounded up. The effective stack is capped by the requested maximum tiers and by the usable trailer height. Auto orientation calculates both rotations and chooses the shorter floor length.

Mixed lines are packed deterministically. Each floor position becomes a placement with a width and a depth. Deeper placements are sorted first, and each one goes into the first existing row where its width still fits; otherwise it starts a new row. The row depth is the deepest placement in that row. This is an estimate, not a CAD load plan.

Pounds per linear foot is total gross weight divided by linear feet. The calculator reports it because some LTL tariffs use a linear-foot or capacity rule. The trigger and minimum charge vary by carrier, contract, and service, so the calculator does not apply a threshold. The 53 ft, 48 ft, and 28 ft trailer profiles use typical planning dimensions of 636 × 100 × 110 in, 576 × 100 × 110 in, and 336 × 100 × 110 in. They are not manufacturer specifications, and every dimension is editable.

Density and class are secondary outputs in the linear feet calculator. They use total gross weight and total cube, not linear feet, so stacking can reduce floor use without changing density or class.

Parcel dimensional weight

The dimensional weight calculator is a separate model. It uses the parcel’s measured sides, rounds each one up to the next whole inch, multiplies the rounded sides, and divides by the carrier divisor:

rounded side = ceil(measured side)
cube (in³) = rounded length × rounded width × rounded height
DIM weight (lb) = ceil(cube ÷ divisor)
billable weight (lb) = max(actual weight, DIM weight)

The whole-inch round-up is effective August 18, 2025 at UPS and FedEx, and is part of the current USPS dimensional-weight steps. Rounding happens before the cube calculation, not after.

The listed divisors are 139 for UPS Daily Rates, 166 for UPS Retail Rates, 139 for FedEx Express and Ground list rates, and 139 for USPS. A custom divisor can be entered for a contract or a service guide that differs. The calculator does not invent a divisor when the rate basis is unknown.

USPS threshold, cap, and shape factor

Since July 12, 2026, USPS applies dimensional weight only when the parcel exceeds 1,728 in³ (1 ft³). The dimensional weight is capped at 70 lb. A non-rectangular parcel multiplies its measured cube by 0.785 before the 1,728 in³ test and the divisor. The calculator applies that factor only to USPS; UPS and FedEx use the rectangular bounding box.

USPS can also add nonstandard length or cube fees. The calculator flags a longest side over 22 in, a measured or adjusted cube over 2 ft³, length + girth over 108 in (Priority Mail), and length + girth over 130 in (Ground Advantage). Those flags are notices, not price quotes. The DMM and Notice 123 control the actual charge, and a parcel over 130 in combined length and girth is outside USPS parcel limits.

Break-even and reverse solver

Break-even density is the density at which actual weight equals dimensional weight:

break-even density (lb/ft³) = 1,728 ÷ divisor

At divisor 139, the break-even is 12.43 lb/ft³. At divisor 166, it is 10.41 lb/ft³. Below the break-even, DIM weight is higher and sets the bill; above it, actual weight wins. The calculator also shows the cube reduction needed to make actual weight win, and converts that reduction into a height reduction assuming all of the change comes from the parcel height. That is a planning estimate, not a packaging instruction.

Parcel limits and accessorials are separate from DIM weight. The calculator flags a longest side over 108 in, length plus girth over 165 in, a longest side over 48 in, a second-longest side over 30 in, length plus girth over 105 in, and an actual weight over 50 lb. Carrier tariffs control whether a particular flag becomes a charge.

NMFC commodity reference

The NMFC commodity lookup is a planning reference, not a reproduction of the NMFC. It covers 40 commodities in 12 categories. Each entry records the classification basis, an estimated packed-density range, the handling flags, the reclass risk, and the measurement and packaging questions that change the answer.

Class spans are not hand-entered. The endpoints of each density estimate are mapped through the 13-tier scale in the freight-class module, and the page shows every class the range touches. A 2–4 lb/ft³ estimate spans Class 250 at 2.0 and Class 175 at 4.0. The span is a planning range for the endpoints, not a prediction that every shipment lands in every class. The chart, the calculator, and the commodity lookup use the same scale, so they cannot disagree.

We do not publish NMFC item numbers from memory or from a public list that may predate the 2025 consolidation. A wrong item number on a BOL is worse than no number. Confirm the current item in ClassIT+ or with the carrier before booking.

A category page is generated only when a category has at least 3 commodity guides. Smaller categories link to a filtered directory instead, which avoids thin category pages. The reference was reviewed on November 11, 2026 (version 2026.11). Each entry carries the review date and its source list, and a correction that changes a class span is reviewed before the page is updated.

Known limits

Data handling

The calculator runs entirely in your browser. Shipment values are not sent to a FreightClassHub server and are not stored in an account or database. A share link encodes the shipment into the URL itself, so anyone with the link can read those values. Editing a shared shipment removes the encoded parameter from the address bar.

There are no advertising scripts or analytics at launch. Fonts are self-hosted. See the privacy policy for the full description, including hosting logs.

Sources

• NMFTA — new effective date for the 2025 NMFC changes: the July 19, 2025 effective date and the 13-tier density scale.
• NMFTA — NMFC classification and ClassIT+: the official classification system and the 18-class structure.
• Estes — freight class and density calculator: carrier measurement and density conventions.
• FedEx Freight — freight class calculator: carrier measurement and class reference.
• USPS DMM 123 — Priority Mail dimensional weight: the 1,728 in³ threshold, divisor 139, 70 lb cap, whole-inch round-up, and 0.785 non-rectangular factor.
• USPS DMM 201 — physical standards: the 108 in combined length + girth limit and the 130 in Ground Advantage oversized allowance.
• USPS DMM 283 — Ground Advantage: Ground Advantage eligibility and dimensional-weight application.
• UPS — dimensional weight: UPS Daily divisor 139, UPS Retail divisor 166, and whole-inch measurement.
• FedEx — dimensional weight: FedEx divisor 139 and whole-inch rounding.
• PHMSA — hazardous materials: federal hazmat rules referenced by the commodity handling flags.

Corrections

If a number, source, or explanation is wrong, send the page URL and the correction to hello@freightclasshub.com. Corrections that change a calculation or a class result are reviewed against the NMFC and carrier references before the page is updated.