Dimensional Weight Calculator

What dimensional weight is

Carriers price parcels by space as well as weight. A large, light box takes as much room on a truck as a heavy one, so carriers calculate a dimensional (DIM) weight from the box's size and charge the higher of the dimensional and actual weights, called the billable weight. Using a box that is too big for the item can double the price of a label.

DIM weight (lb) = length × width × height (inches) ÷ divisor
Metric: DIM weight (kg) = L × W × H (cm) ÷ divisor
Billable weight = the larger of DIM weight and actual weight, rounded up

Divisors used by carriers

• UPS and FedEx commonly use 139 for US domestic daily rates; some retail rates use 166.
• USPS applies dimensional weight only to packages larger than 1 cubic foot (1,728 cubic inches). Under its 2026 rule change, reported for July 12, 2026, USPS moved from 166 to 139 for Priority Mail, Priority Mail Express, Ground Advantage and Parcel Select, and rounds each dimension up to the next inch.
• International and many metric couriers often use 5,000 (cm³ per kg); some use 6,000.

Divisors change with carrier price updates and depend on your contract, so check your carrier's current rate guide.

Worked examples

• A box of 18 × 14 × 12 inches holds 3,024 cubic inches (1.75 cu ft). At 139 its DIM weight is 21.76 lb, rounded up to 22 lb. If the contents weigh 8 lb, you pay for 22 lb, 14 lb more than the actual weight. At a 166 divisor it would bill 19 lb.
• A 12 × 12 × 12 box (exactly 1 cubic foot) weighing 4 lb has a DIM weight of 12.43 lb, rounded to 13 lb. UPS or FedEx would bill 13 lb; USPS bills the actual 4 lb, because the box is not larger than 1 cubic foot.
• A 40 × 30 × 20 cm parcel weighing 3 kg with a 5,000 divisor has a DIM weight of 4.8 kg, billed as 5 kg (rounded up to the next half kilogram in this calculator).

How to lower shipping costs

• Use the smallest box that protects the item. Cutting an inch from each side of the 18 × 14 × 12 box to 17 × 13 × 11 reduces DIM weight from 22 lb to 18 lb at 139.
• Consider poly mailers for soft goods such as clothing.
• Use flat-rate options for small, heavy items, where they are cheaper than weight-based rates.
• Compare carriers for large, light parcels, since divisors and thresholds differ.

Measuring correctly

Measure the outside of the box at its longest points, including any bulges, and round each measurement up to the next whole inch (or centimetre). Weigh the packed box on a shipping scale and round up to the next pound. Carriers re-measure parcels, and adjustments for under-declared sizes are billed to the shipper.

Checking box sizes before you buy

If you ship the same products often, run your common box sizes through the calculator once and keep a list of the billable weight for each. For a carrier using 139, any box over 1,529 cubic inches (11 × 139) is billed as at least 12 lb, whatever it weighs. Choosing from two or three well-fitting box sizes usually saves more than negotiating rates.

Oversize and additional handling

Very long or heavy parcels can also trigger additional handling or oversize surcharges on top of the billable weight, based on the longest side, length plus girth or actual weight. If a parcel is close to those limits, check the carrier's surcharge rules before choosing a box.

Common mistakes

• Using inside dimensions. Carriers measure the outside.
• Not rounding up. Fractions of an inch or pound are rounded up.
• Assuming USPS ignores box size. Boxes over 1 cubic foot are billed by DIM weight.

Frequently asked questions

Sources

• UPS. Determining billable weight: dimensional weight (ups.com).
• FedEx. Dimensional weight calculation (fedex.com).
• USPS. Notice 123 price list and Domestic Mail Manual: dimensional weight pricing (usps.com, pe.usps.com).

Last reviewed 27 October 2026. Results are estimates; see our disclaimer.