Dimensional Weight

What it means

The formula is the same everywhere. Only the units and the divisor change. Multiply the three outside dimensions to get the volume, then divide by the carrier's divisor. The divisor is the volume the carrier treats as one unit of weight, such as cubic inches per pound or cubic centimeters per kilogram.

Chargeable weight is the number the carrier actually rates. Maersk describes it as the higher of the actual (gross) weight and the volumetric weight, which is also called dimensional or volume weight.^[3] A smaller divisor makes the dimensional weight larger, so the same box costs more to ship.

Common DIM divisors

The divisor is set by the carrier or the service, not by a law of physics. These are the published figures we could confirm:

USPS changed its DIM factor to 139 effective July 12, 2026. The rule covers Priority Mail Express, Priority Mail, USPS Ground Advantage (retail and commercial) and Parcel Select, for parcels to zones 1 through 9 that exceed 1 cubic foot (1,728 cubic inches).^[1] Before that, a 2018 Postal Bulletin set a DIM divisor of 166 for Priority Mail Express, Parcel Select and Priority Mail, using the same 1-cubic-foot threshold.^[2] Many older guides and calculators still show 166.

For air freight, Maersk calls 6,000 an industry standard set by IATA. It also notes that some carriers use 5,000, which charges bulky cargo more, and that express carriers have their own formulas that can vary by origin and destination.^[3] UPS, FedEx and other parcel carriers publish their own divisors. Check the current service guide or your contract, because negotiated divisors are common.

USPS rounding rules

Rounding changes the answer, so follow the carrier's steps in order. Under the 2026 USPS rule:^[1]

1. Measure length, width and height in inches.
2. Round each dimension up to the nearest whole inch.
3. Multiply the three numbers.
4. If the result is 1,728 cubic inches or less, DIM pricing does not apply under this rule.
5. If it is more, divide by 139 and round up to the next whole pound.

The same steps apply to nonrectangular parcels under the 2026 bulletin.^[1] The 2018 rules rounded each measurement off to the nearest inch rather than up, so the same box can now measure larger.^[2]

Why it matters

Dimensional weight is often the biggest reason a parcel or air invoice comes in higher than the quote. A carton that is a few inches too big can add several billable pounds, and the change is easy to miss because the scale weight did not move. Picking a box that fits the product, cutting empty space and consolidating small cartons into one can lower chargeable weight.^[3] Run the numbers before you ship with the dimensional weight calculator. RapidShips runs a warehouse dock in East Brunswick, NJ, and is not a parcel carrier or airline, so the carrier's published rules and your contract set the actual billable weight.

Parcel vs air vs LTL

• Parcel. Dimensional weight is a core part of the price. Every box is measured or scanned, and a light box in a large carton can be billed on its dimensional weight instead of its scale weight.
• Air cargo. Chargeable weight is the higher of actual and volumetric weight, almost always in kilograms with a 6,000 or 5,000 divisor.^[3] To get volume in cubic meters first, use the CBM calculator.
• LTL freight. Most LTL is not priced by a DIM divisor. It is priced by weight and freight class. NMFTA lists density as one of four class factors, along with handling, stowability and liability, and classes run from 50 to 500. Denser freight usually gets a lower class and a lower cost.^[4] So size still matters in LTL, through class rather than a dimensional weight. See how LTL freight is priced and the freight class calculator.

Example

Illustrative only, not a real shipment or quote. A USPS Priority Mail box measures 17.25 x 13.5 x 11.75 inches and weighs 9 lb. Round each side up: 18 x 14 x 12 = 3,024 cubic inches. That is over 1,728, so DIM applies. 3,024 / 139 = 21.76, which rounds up to 22 lb. The box is billed at 22 lb, not 9 lb. At the older 166 divisor the same volume would give 18.2, or 19 lb.

Illustrative air example. A pallet measures 120 x 80 x 100 cm and weighs 110 kg. 120 x 80 x 100 = 960,000 cubic centimeters. 960,000 / 6,000 = 160 kg, so the chargeable weight is 160 kg. With a 5,000 divisor it would be 192 kg. Maersk gives a similar case: a 50 kg package of 100 x 60 x 30 cm has a volumetric weight of 30 kg, so it is charged at 50 kg.^[3]

Frequently asked questions