USPS vs FedEx dimensional weight: side-by-side numbers
USPS and FedEx both divide by 139 for dimensional weight, but they differ in when it applies and how they round: USPS only bills dimensional weight above 1,728 in³ and rounds each side up, while FedEx applies it to all sizes and rounds each side to the nearest inch.
Rules side by side
| USPS | FedEx | |
|---|---|---|
| Divisor | 139 | 139 |
| Applies above | 1,728 in³ | all sizes |
| Each dimension rounded | up to the next inch | to the nearest inch |
| Scope | Priority Mail (commercial) and Parcel Select, rectangular parcels. Nonrectangular parcels use a 0.785 volume factor and divisor 166. | U.S., Puerto Rico and international shipments, as stated on the FedEx page. |
Same boxes, both carriers
| Outside, in | USPS DW, lb | FedEx DW, lb |
|---|---|---|
| 10 × 8 × 6 | n/a | 4 |
| 12 × 12 × 12 | n/a | 13 |
| 12.5 × 11.5 × 11.5 | 14 | 14 |
| 14 × 10 × 8 | n/a | 9 |
| 16 × 12 × 10 | 14 | 14 |
| 18 × 14 × 12 | 22 | 22 |
| 20 × 16 × 12 | 28 | 28 |
| 24 × 18 × 18 | 56 | 56 |
| 16.4 × 12.4 × 10.6 | 18 | 16 |
| 30 × 20 × 20 | 87 | 87 |
Fractional sizes show where rounding rules diverge. Packgent rounds the FedEx result up to the next pound; FedEx's page does not state result rounding. Checked 2026-10-27.