Dimensional Weight: USPS, UPS and FedEx
By Selling Fee Tools team ·
A large, light box takes up as much room in a truck as a heavy one, so carriers charge by size as well as weight. Dimensional weight (DIM weight) is a weight worked out from a package’s size. The carrier charges for whichever is greater, the dimensional weight or the actual weight: the billable weight. This guide covers the rules for USPS, UPS and FedEx in the US, checked in October 2026.
The formula
Length × width × height (inches) ÷ divisor, rounded up to the next whole pound.
An 18 × 14 × 8 inch box is 2,016 cubic inches. Divided by 139 that is 14.5, so 15 lb. If the box actually weighs 4 lb, the carrier charges for 15 lb.
Divisors by carrier
| Carrier | Divisor | How sides are measured |
|---|---|---|
| USPS Priority Mail and Ground Advantage | 139 | Each side rounded up to the next whole inch |
| UPS Daily Rates (business account) | 139 | Measured size, no per-side rounding in UPS’s guidance |
| UPS Retail Rates | 166 | As above |
| FedEx (US) | 139 | Each side rounded to the nearest whole inch |
A bigger divisor gives a lower dimensional weight: the same box has a lower billable weight at UPS Retail Rates (166) than at Daily Rates (139), though the price per pound differs between the two.
The USPS rules
- USPS only uses dimensional weight for parcels over one cubic foot, 1,728 cubic inches, after each side is rounded up. Smaller parcels are charged on actual weight.
- For a tube or other non-rectangular parcel, USPS multiplies the volume by 0.785 first.
- If the dimensional weight is over 70 lb, you pay the 70-pound price.
These come from the USPS Domestic Mail Manual, revised in July 2026.
Make the box smaller
Every inch counts three times over, once in each direction. Taking an 18 × 14 × 8 box down to 16 × 12 × 6:
- cuts the volume from 2,016 to 1,152 cubic inches, below the USPS one-cubic-foot line, so USPS charges actual weight;
- cuts the FedEx dimensional weight from 15 lb to 9 lb.
Use the smallest box the product fits safely, and poly mailers for soft goods.
Marketplace fulfillment uses it too
Fulfillment services apply the same idea. Walmart Fulfillment Services uses the greater of the unit weight and the dimensional weight (L × W × H ÷ 139) for items from 1 lb, adds 0.25 lb of packaging and rounds up, then charges by that shipping weight. A 1.2 lb item in a 10 × 8 × 3 in box ships at 2 lb, $4.95.
Tools
- Dimensional weight calculator: billable weight for USPS, UPS and FedEx side by side, with each carrier’s rounding
- Walmart fee calculator: WFS fulfillment fees from your product’s weight and box
- Landed cost calculator: freight and duty per unit for imports
Sources: USPS Domestic Mail Manual, UPS and FedEx dimensional weight pages and Walmart’s Marketplace pricing page, listed on each tool and on our methodology page.