Why carriers charge for space
A large box of pillows weighs little but fills a truck. To be paid for the space a parcel takes, carriers compute a dimensional weight (DIM weight) from its volume and bill whichever is greater: the actual weight or the dimensional weight. That figure is the billable weight.
The formula
DIM weight (lb) = length × width × height (in) ÷ divisor
| Carrier and service | Divisor |
|---|---|
| UPS and FedEx daily rates | 139 |
| UPS and FedEx retail rates, USPS | 166 |
| International express (metric) | 5,000 cm³ per kg |
UPS and FedEx round each dimension up to the next whole inch, then round the result up to the next whole pound. USPS applies dimensional pricing to parcels larger than one cubic foot (1,728 cubic inches).
Example
An 18 × 12 × 10 in box contains 2,160 cubic inches. Divided by 139, that is 15.54 lb, which rounds up to 16 lb. If the contents weigh 8 lb, you pay for 16 lb: the box is twice as expensive to ship as its weight suggests.
Size limits
Carriers also cap a parcel’s size with length plus girth: the longest side plus twice the sum of the other two. For the box above that is 18 + 2 × (12 + 10) = 62 in.
- USPS: 108 in maximum for most services, 130 in for Ground Advantage oversized.
- UPS and FedEx Ground: 165 in maximum, with surcharges well before that.
How to lower the bill
- Use the smallest box that protects the item; a two-inch reduction on each side often saves several billable pounds.
- Poly mailers and padded envelopes beat boxes for soft goods.
- Combine items into one parcel only when the result is still dense.
- Negotiated contracts can raise the divisor, which lowers DIM weight.
Enter centimeters and kilograms when you use the 5,000 divisor for international shipments.