USPS dimensional weight change (July 2026): 166 to 139
On 12 July 2026 USPS cut its DIM divisor from 166 to 139 and began rounding every fractional inch up. What it costs per box size, and how to adjust your packaging.
Updated 2026-09-30
What changed
- Divisor 166 → 139 for Priority Mail, Priority Mail Express, USPS Ground Advantage and Parcel Select. A lower divisor means a higher dimensional weight: about 19% more for the same box.
- Fractions round up. A 12.1 inch side is now billed as 13 inches, not 12.
- The 1 cubic foot line stays. Boxes of 1,728 cubic inches or less are still billed on actual weight. Because of the round-up, a box measuring 12.25 inches per side now counts as 13 × 13 × 13 and crosses the line.
What it costs, box by box
DIM weight before and after the change, for common boxes over 1 cubic foot:
| Box (in) | Before (166) | Now (139) | Increase |
|---|---|---|---|
| 14 × 14 × 14 | 17 lb | 20 lb | +3 lb |
| 15 × 12 × 10 | 11 lb | 13 lb | +2 lb |
| 16 × 12 × 12 | 14 lb | 17 lb | +3 lb |
| 16 × 16 × 16 | 25 lb | 30 lb | +5 lb |
| 18 × 12 × 12 | 16 lb | 19 lb | +3 lb |
| 18 × 14 × 12 | 19 lb | 22 lb | +3 lb |
| 18 × 18 × 12 | 24 lb | 28 lb | +4 lb |
| 18 × 18 × 18 | 36 lb | 42 lb | +6 lb |
| 20 × 12 × 12 | 18 lb | 21 lb | +3 lb |
| 20 × 14 × 10 | 17 lb | 21 lb | +4 lb |
| 20 × 20 × 20 | 49 lb | 58 lb | +9 lb |
| 22 × 18 × 12 | 29 lb | 35 lb | +6 lb |
| 24 × 12 × 12 | 21 lb | 25 lb | +4 lb |
| 24 × 18 × 16 | 42 lb | 50 lb | +8 lb |
| 24 × 20 × 18 | 53 lb | 63 lb | +10 lb |
| 24 × 24 × 24 | 84 lb | 100 lb | +16 lb |
| 30 × 20 × 20 | 73 lb | 87 lb | +14 lb |
How to adjust
- Re-measure your standard boxes in whole inches, rounding up. Anything that was quoted at 12.1 inches is now 13.
- Aim for 1 cubic foot or less on USPS where the product allows. At or below 1,728 cubic inches, USPS still ignores dimensional weight entirely.
- Move soft goods to poly mailers. Flexible packaging is usually billed on weight.
- Compare carriers again. USPS lost part of its advantage for light, bulky parcels. With everyone at 139, the rate per pound decides, so compare commercial rates rather than retail.
Run your own boxes through the USPS dimensional weight calculator.