Dimensional weight calculator
Billable weight from box size and actual weight, with the USPS 139 divisor or your carrier's, plus cubic feet and CBM.
- ๐บ๐ธ US federal & state rules
- USPS DMM 223 and 283, section 1.4
- See sources
Billable weight per box
22 lb
Dimensional weight is higher, so you pay for size
- Dimensional weight
- 22 lb
- Actual weight
- 8 lb
- Cubic feet
- 1.75
- CBM
- 0.0496
This is an example. Enter your numbers above and press the button to see your own result.
- USPS rule for Priority Mail and Ground Advantage to zones 1 to 9: each side is rounded up to the next whole inch, and the volume is divided by 139 once it passes 1 cubic foot.
- Odd-shaped parcels (tubes, rolls) use a 0.785 adjustment at USPS. This calculator assumes a rectangular box.
Show the math
| Size used | 18 ร 14 ร 12 in |
|---|---|
| Cubic inches | 18 ร 14 ร 12 = 3,024 |
| Dimensional weight | 3,024 รท 139 = 21.76, rounded up to 22 lb |
| USPS threshold | Over 1,728 cubic inches, dimensional weight applies |
| Billable weight | Greater of 8 lb actual and 22 lb dimensional = 22 lb |
What to do next
How it works
Carriers price space as well as weight. The calculator multiplies the three sides in inches, divides by the divisor and rounds up to a whole pound. The billable weight is whichever is higher, that number or the actual weight rounded up.
For USPS it follows the Domestic Mail Manual: each side is rounded up to a whole inch, the divisor is 139, and dimensional weight only applies once the box is over 1 cubic foot. For other carriers, enter the divisor from your rate guide.
Things to keep in mind
Measure the outside of the box at its longest points, including any bulge. A box that measures 12.2 inches is treated as 13.
Cubic feet and CBM are shown too, which is what freight forwarders and ocean shippers usually quote by.
Sources
Rules applied as of 2026-10-19. See the sources below for details.
Frequently asked questions
How do I calculate dimensional weight?
Multiply length, width and height in inches, then divide by the carrier's divisor and round up. An 18 by 14 by 12 inch box is 3,024 cubic inches, which is 22 lb at USPS's 139 divisor.
When does USPS charge dimensional weight?
For Priority Mail and Ground Advantage, only when the box is over 1 cubic foot (1,728 cubic inches) and going to zones 1 to 9. A 12 inch cube is exactly 1,728 and is charged by actual weight.
What is billable weight?
It is the larger of the actual weight and the dimensional weight, each rounded up to the next pound. A light but large box is billed by size.
How do I lower dimensional weight?
Use the smallest box that fits. Cutting a box from 18 by 14 by 12 to 16 by 12 by 10 inches drops USPS dimensional weight from 22 lb to 14 lb.