Dimensional weight calculator
Size or scale: find out which one the carrier bills.
Measure the outside of the packed box at its longest points. Divisors checked October 27, 2026; they change by carrier and contract.
What is dimensional weight?
Dimensional weight, also called DIM or volumetric weight, is a price weight a carrier computes from a package's size instead of its scale weight. Volume is divided by a number called the divisor, and you are billed for the greater of that figure and the actual weight. A 20 × 15 × 12 inch box that weighs 10 pounds has a volume of 3,600 cubic inches; divided by 139 that is 25.9, rounded up to 26 pounds, so the carrier bills 26 pounds.
What is the dimensional weight formula?
Length × width × height, each rounded up to a whole inch, divided by the divisor, with any fraction of a pound rounded up. In centimeters the divisor is 5,000 and the answer is in kilograms. UPS, FedEx and the Postal Service all describe the same three steps: measure, divide, compare with the actual weight and bill the greater.
What is the divisor for UPS, FedEx and USPS in 2026?
UPS: 139 for Daily Rates and for U.S. export and import shipments, and 166 for Retail Rates on domestic shipments (UPS 2026 Rate & Service Guide, updated September 7, 2026). FedEx: 139 for U.S., Puerto Rico and international shipments, except 166 for FedEx International Deferred Freight (FedEx Service Guide 2026, page 135). USPS: 139 for Priority Mail and USPS Ground Advantage Commercial, for parcels over 1 cubic foot (Domestic Mail Manual 123.1.3 and 283.1.4, which show a July 12, 2026 revision mark). The calculator offers each one, plus a custom divisor. We checked these on October 27, 2026; carriers change divisors, and contract rates often differ, so use the number on your own rate sheet.
Do carriers round the measurements?
Yes, and it matters. UPS says to measure each side at its longest point and round any fraction up to the next whole inch, with a one-inch minimum (1.1 counts as 2). FedEx has rounded any fraction of an inch up since August 18, 2025. USPS rounds each measurement up too. A box measured 10.2 × 8 × 6 inches is billed as 11 × 8 × 6: 528 cubic inches, 3.8 at 139, 4 pounds, instead of the 3.5 pounds that the raw measurements would suggest.
Does USPS use dimensional weight on every package?
No. For Priority Mail and Ground Advantage Commercial it applies only to parcels larger than 1 cubic foot (1,728 cubic inches), and the dimensional weight is capped at 70 pounds. A 12 × 12 × 12 inch box is exactly 1,728 cubic inches, so it is billed on its actual weight (3 pounds in our example). A 40 × 30 × 20 inch parcel would work out to 172.7 pounds, but the customer pays the 70-pound price. For a nonrectangular parcel USPS multiplies length × width × height by 0.785 before dividing.
How can I lower dimensional weight charges?
Shrink the box. Every inch counts twice, because each side is rounded up and the three sides are multiplied. In the UPS example a 20 × 15 × 12 inch box bills as 26 pounds at 139; if the same parcel moves at the Retail divisor of 166 it bills as 22. Use a box that fits the item with little void fill, a poly mailer for soft goods, and ask the carrier whether a negotiated divisor applies to your account.
Why do international shipments use 5,000?
A divisor of 5,000 turns cubic centimeters into kilograms: 1,000,000 cm³ is a cubic meter, and 200 kg per cubic meter is the density at which the dimensional and actual weights are equal. FedEx Canada gives the formula as length × width × height in centimeters ÷ 5,000, rounded up. A 50 × 40 × 30 cm box is 60,000 cm³, exactly 12 kilograms, and the calculator does not round that up to 13. Some carriers use other divisors for some services (FedEx lists 166 for one international freight service), so check the rate guide.
How the calculator works
Enter the three sides, the actual weight and the rate type. The calculator rounds each side up to the next whole unit (never below 1), multiplies, divides by the divisor, rounds up, and compares the result with the actual weight, which UPS and FedEx also round up to a whole pound. The larger number is the billable weight. The table shows each step, the density of your package, and the density at which the two weights are equal: 1,728 ÷ 139 = 12.4 pounds per cubic foot at 139, 10.4 at 166. A package denser than that is billed by its weight; a lighter one is billed by its size. Dense items such as books or cans are mostly billed on the scale; pillows and empty-looking boxes on the tape measure.
Worked example
A 20 × 15 × 12 inch box weighing 10 pounds has a volume of 3,600 cubic inches. At UPS Daily Rates (divisor 139) that is 25.9, so 26 pounds; at the Retail divisor (166) it is 21.7, so 22 pounds. Either way the size decides, not the 10 pounds on the scale. A compact 10 × 10 × 10 inch box that weighs 30.2 pounds has a dimensional weight of 8 pounds, but its actual weight rounds up to 31, and 31 pounds is what UPS bills.
Common mistakes
Using one divisor for every carrier is the biggest one: UPS Retail Rates use 166 while UPS Daily Rates, FedEx and USPS use 139, so the same box can produce different answers. Measuring the inside of the box rather than the outside, forgetting to round up each side, and ignoring bulges all lead to bills that differ from the estimate. Carriers re-measure packages and may adjust charges; FedEx says package shape and dimensions can change in transit, which can change the dimensional weight. Finally, dimensional weight is only the weight used to price the shipment; surcharges for large packages, extra handling and residential delivery are separate, and this calculator does not estimate them.
Limits of this method
The divisor is a pricing rule, not a law of physics, and it changes by carrier, service, country and contract. FedEx has rounded any fraction of an inch up only since August 18, 2025, and the Postal Service manual now shows 139 where an older USPS guide still shows 166, so a figure from a blog post written two years ago may be wrong. Negotiated accounts often carry their own divisors, and freight services bill by pallet or handling unit with different rules. Treat the result as an estimate and confirm it against the carrier's rate calculator or your agreement before you quote shipping to a customer.
Sources, all read October 27, 2026: UPS, 2026 UPS Rate & Service Guide, U.S. 48, Alaska & Hawaii, Daily Rates and Retail Rates (updated September 7, 2026), “Determine the Weight and Size”; FedEx Service Guide 2026 (effective January 5, 2026, updated September 11, 2026), “Dimensional Weight,” page 135; FedEx Canada, “About Dimensional Weight”; U.S. Postal Service, Domestic Mail Manual sections 123.1.3 and 283.1.4. An estimate for planning: your carrier’s invoice decides. Related: weight converter, cubic feet calculator, pounds to kilograms, unit price calculator. How we check our calculators.