Dimensional Weight Calculator
You pay for 14 lb more than the box weighs. A smaller box would cut the billable weight.
How the dimensional weight calculation works
A package's dimensional weight and billable weight using each carrier's own divisor and rounding: 139 for UPS daily rates, FedEx and USPS, 166 for UPS retail rates, or a custom divisor.
Measure and round each side
Measure in inches at the longest points. FedEx and USPS round each fraction of an inch up; UPS rounds to the nearest inch (18.5 becomes 19, 18.4 becomes 18). An 18 × 14 × 12 in box is 3,024 cubic inches.
Divide by the carrier's DIM divisor
3,024 ÷ 139 = 21.76, rounded up to 22 lb. USPS uses the same 139 divisor, but only for parcels over 1,728 cubic inches. On UPS retail rates the divisor is 166, so the same box is 3,024 ÷ 166 = 18.22, rounded up to 19 lb.
Billable weight is the higher of the two
The box weighs 8 lb but has a 22 lb dimensional weight, so the carrier charges for 22 lb.
Check the divisor in your contract
Negotiated accounts often have a higher divisor, which lowers dimensional weight. Enter it as a custom divisor.
Worked example. An 18 × 14 × 12 in box weighing 8 lb has a volume of 3,024 cubic inches. Divided by 139 that is 21.76, rounded up to 22 lb, so the billable weight is 22 lb.
Dimensional Weight FAQ
How do I calculate dimensional weight?
Multiply length × width × height in inches and divide by the carrier's divisor. 18 × 14 × 12 ÷ 139 = 21.76, which UPS, FedEx and USPS round up to 22 lb.
What is dimensional weight?
A weight based on the space a box takes up rather than what it weighs. Carriers charge for the dimensional weight or the actual weight, whichever is higher, so large light boxes cost more to ship. It is also called DIM weight or volumetric weight.
What DIM divisor do UPS and FedEx use?
Both use 139 for US parcels on their standard (daily or list) rates. UPS retail rates, charged to shippers without daily rates and at The UPS Store, use 166 for domestic parcels. Contract accounts may have a different divisor, so check your rate agreement.
What is the USPS dimensional weight divisor?
USPS uses 139 for Priority Mail and Ground Advantage parcels (it was 166 before 12 July 2026). It applies dimensional weight only to parcels larger than one cubic foot (1,728 in³); smaller boxes are priced on actual weight. If the dimensional weight is over 70 lb, you pay the 70 lb price.
Do carriers round the box dimensions?
Yes. FedEx and USPS round each fraction of an inch up to the next whole inch. UPS rounds each side to the nearest whole inch, so 1.50 to 1.99 in counts as 2 in, with a minimum of 1 in. All three round the dimensional weight up to the next whole pound.
What is billable weight?
The weight the carrier charges for: the higher of the actual weight and the dimensional weight, each rounded up to the next pound.
How can I lower dimensional weight charges?
Use the smallest box that protects the item, cut down oversized boxes, or switch to poly mailers for soft goods. Every inch removed from each side reduces the volume.
Sources: UPS Rate and Service Guide, daily rates: determine the weight and size · UPS Rate and Service Guide, retail rates: 166 domestic divisor · FedEx Service Guide 2026: dimensional weight · USPS DMM 283.1.4: Ground Advantage dimensional weight · USPS DMM 223.1.4: Priority Mail dimensional weight