What changed in the USPS dimensional weight rules?
| Rule | Before 12 July 2026 | From 12 July 2026 |
|---|---|---|
| Divisor (DIM factor) | 166 | 139 |
| Each side of the box | Rounded off to the nearest whole inch | Rounded up to the next whole inch |
| DIM weight applies to parcels over | 1,728 in³ | 1,728 in³ (unchanged) |
The change covers Priority Mail Express, Priority Mail, USPS Ground Advantage and Parcel Select, retail and commercial. USPS says it’s “for consistency with industry standards”: UPS and FedEx also divide by 139.
Sources: USPS Postal Bulletin 22705 (effective 12 July 2026); current rule in DMM 113.1.3; previous rule (166, round off) in the archived DMM 113, June 2026. Checked 10 Oct 2026.
How is USPS dimensional weight calculated?
- Measure length, width and height in inches at the widest points of the sealed box.
- Round each one up to the next whole inch: 12.1 in counts as 13 in.
- Multiply them to get the cubic size.
- If that’s 1,728 cubic inches or less, stop: USPS charges the actual weight.
- If it’s more, divide by 139 and round up to the next whole pound. That’s the dimensional weight.
- Billable weight is the greater of the actual weight and the dimensional weight.
For tubes and other non-rectangular parcels, USPS multiplies the cubic size by 0.785 before applying the same 1,728 test and 139 divisor (DMM 113.1.3).
Worked example: the same box, before and after
A 4 lb item in a box measuring 14.2 × 12 × 10.4 inches:
| Step | Before (166, round off) | Now (139, round up) |
|---|---|---|
| Sides used | 14 × 12 × 10 in | 15 × 12 × 11 in |
| Cubic size | 1,680 in³ | 1,980 in³ |
| Over 1,728 in³? | No | Yes |
| Dimensional weight | not applied | 1,980 ÷ 139 = 14.2 → 15 lb |
| Billable weight | 4 lb | 15 lb |
The box didn’t change. Rounding up pushed it over the 1-cubic-foot line, and the lower divisor made its DIM weight heavier. A box that was already over the line moves less: 16 × 12 × 10 in (1,920 in³) went from 12 lb (1,920 ÷ 166 = 11.6) to 14 lb (1,920 ÷ 139 = 13.8).
Does the USPS change affect small parcels?
No. Parcels of 1,728 cubic inches or less are still priced by actual weight. That’s a real difference from UPS: its rate guide says dimensional weight may apply to all UPS domestic and international package services, and divides the cubic size by 139 (UPS Rate and Service Guide). FedEx divides by 139 for US, Puerto Rico and international shipments (FedEx: what is dimensional weight). Contract rates can use a different divisor, so check yours.
How to keep USPS DIM charges down
- Measure the sealed box, bulges included. With rounding up, you can’t round your way under the line any more.
- Stay at or under 1,728 in³ where the product allows. A 12 × 12 × 12 in box is exactly 1,728 in³, so it’s priced by actual weight.
- Above the line, every 139 in³ adds a pound. In the example, cutting the 11 in side to 10 in (1,800 in³) still bills 13 lb; a 14 × 12 × 10 in box (1,680 in³) drops back to the actual 4 lb.
- Compare carriers per box. The same box can bill differently at USPS, UPS and FedEx. Easyship affiliate link compares courier rates and prints labels in one place.