Updated July 2, 2026
Check your box's billable weight
Find out whether your box's DIM weight is quietly adding to the bill.
Working Out Your DIM Number
Dimensional (DIM) weight equals length times width times height in inches, divided by the carrier's DIM divisor; UPS and FedEx use 139 for domestic shipments, and USPS uses 166 today, moving to 139 on July 12, 2026. A 14x12x10-inch box has a volume of 1,680 cubic inches; divided by 139, that is 12.1 lbs of DIM weight, so a package that actually weighs 4 lbs is billed at 12.1 lbs. Whichever is higher, DIM weight or actual weight, is what the carrier charges.
The divisor is also called the DIM factor. It exists so carriers can recover the cost of truck and aircraft space: a pillow weighing 1 lb but packed in a cubic-foot box takes up the same volume as a 12-lb book, and DIM weight is how carriers charge accordingly.
Why carriers use DIM weight
Transport vehicles fill up by volume long before they reach their weight limits. A truck full of large, light packages runs out of space just as fast as a truck full of heavy ones. DIM weight pricing discourages shippers from over-boxing and lets carriers recover the real cost of the cubic footage they sell.
Which carriers apply DIM weight, and the USPS change coming July 12, 2026
UPS and FedEx apply DIM weight to all packages where DIM weight exceeds actual weight, using a divisor of 139. USPS currently applies DIM weight only to Priority Mail and Priority Mail Express packages larger than 1 cubic foot (1,728 cubic inches), using a divisor of 166. Per a USPS Newsroom release dated May 11, 2026 and the matching Federal Register filing, USPS is changing that divisor from 166 to 139 across Ground Advantage, Priority Mail, Priority Mail Express and Parcel Select, effective July 12, 2026, to align with the industry standard UPS and FedEx already use. After that date, all three carriers price DIM weight the same way.
Things to know
- Use the smallest box that safely fits the item. Every inch of empty space increases DIM weight.
- Use packaging that conforms to the product shape rather than generic square boxes, where possible.
- For items that are already heavy relative to their size, DIM weight rarely applies. Focus right-sizing effort on light products in large boxes.
- Run the DIM weight calculation before choosing packaging, not after - the DIM weight calculator does this in seconds.
Numbers at a Glance
| Package dimensions | Volume (cu in) | DIM weight (139) | DIM weight (166) |
|---|---|---|---|
| 14 x 12 x 10 in | 1,680 | 12.1 lbs | 10.1 lbs |
| 18 x 14 x 12 in | 3,024 | 21.8 lbs | 18.2 lbs |
| 10 x 8 x 6 in | 480 | 3.5 lbs | 2.9 lbs |
| 24 x 18 x 16 in | 6,912 | 49.7 lbs | 41.6 lbs |
DIM weight rounded to one decimal place. Carriers round up to the next whole pound for billing. Verify current divisors with your carrier before quoting.
Check the billable number before you tape the box shut
Run your own dimensions to see the DIM weight a carrier will actually bill.