Key takeaways
- 1A DIM divisor (or DIM factor) is the cubic inches a carrier treats as one pound: dimensional weight = L × W × H ÷ divisor.
- 2Dividing by 139 instead of 166 raises dimensional weight by about 19%: a 12-inch cube is 12.43 lb at 139 and 10.41 lb at 166.
- 3USPS moved to 139 on July 12, 2026. UPS Daily Rates and FedEx also use 139; UPS Retail Rates use 166.
- 4In metric, 139 in³/lb is about 5,000 cm³/kg and 166 in³/lb is about 6,000 cm³/kg.
- 5The largest box billed at actual weight is the actual weight times the divisor: 695 cubic inches for 5 lb at 139, or 830 at 166.
What a DIM divisor is
Carriers turn a box’s size into a weight so that bulky, light parcels pay for the space they take. The DIM divisor, also called the DIM factor, is the number they divide the cubic size by. It is the number of cubic inches the carrier treats as one pound.
A smaller divisor makes every box count as heavier. When a carrier lowers its divisor, prices on bulky parcels go up without any change to its rate card. That is why the divisor is worth knowing even if you never calculate dimensional weight by hand.
Dimensional weight (lb) = Length × Width × Height (inches) ÷ DIM divisor, rounded up to the next whole pound
Who uses 139 and who uses 166 in 2026
Most small-business shipping in the US now uses 139. The exceptions are UPS Retail Rates and a few freight services.
- Negotiated contracts can use a different divisor. Shippers with high volume sometimes get a higher one, which lowers dimensional weight on every bulky parcel.
| Carrier and rate type | Divisor | Notes |
|---|---|---|
| USPS (Priority Mail Express, Priority Mail, Ground Advantage, Parcel Select) | 139 | Since July 12, 2026; only for parcels over 1 cubic foot |
| UPS Daily Rates | 139 | All domestic and international package services, any size |
| UPS Retail Rates | 166 | Prices at UPS retail locations |
| FedEx (US and most international) | 139 | All shipments in customer packaging |
| FedEx Ground Economy | 139 | Plus its own balloon and oversize rules |
| FedEx International Deferred Freight | 166 | Freight service, not parcels |
139 vs 166 on the same boxes
Because 166 ÷ 139 is about 1.19, dimensional weight at 139 is about 19% higher than at 166 for the same box. After rounding up to whole pounds, the gap is usually 1 to 6 lb on everyday cartons.
- For USPS, boxes of 1 cubic foot or less are billed by actual weight whatever the divisor, so the 10 × 8 × 6, 14 × 10 × 6 and 12-inch cube would be billed at 3, 2 and 5 lb.
| Box (inches) | Actual weight | DIM at 139 | Billed at 139 | DIM at 166 | Billed at 166 |
|---|---|---|---|---|---|
| 10 × 8 × 6 | 3 lb | 3.45 lb | 4 lb | 2.89 lb | 3 lb |
| 14 × 10 × 6 | 2 lb | 6.04 lb | 7 lb | 5.06 lb | 6 lb |
| 12 × 12 × 12 | 5 lb | 12.43 lb | 13 lb | 10.41 lb | 11 lb |
| 18 × 14 × 10 | 6 lb | 18.13 lb | 19 lb | 15.18 lb | 16 lb |
| 24 × 18 × 12 | 15 lb | 37.29 lb | 38 lb | 31.23 lb | 32 lb |
The largest box billed at actual weight
Turn the formula around to find how big a box can be before dimensional weight takes over. Multiply the actual weight, rounded up to a whole pound, by the divisor.
Largest cubic size at actual weight = Actual weight (rounded up) × DIM divisor
| Actual weight | At 139 | At 166 |
|---|---|---|
| 3 lb | 417 in³ | 498 in³ |
| 5 lb | 695 in³ | 830 in³ |
| 10 lb | 1,390 in³ | 1,660 in³ |
| 20 lb | 2,780 in³ | 3,320 in³ |
Metric divisors: 5,000 and 6,000
Outside the US, divisors are usually quoted in cubic centimetres per kilogram. 139 in³/lb converts to about 5,022 cm³/kg, which is why it lines up with the common international divisor of 5,000. 166 in³/lb converts to about 5,997 cm³/kg, close to 6,000. Our dimensional weight calculator works in either system.
Dimensional weight (kg) = Length × Width × Height (cm) ÷ 5,000 (or 6,000)
Free toolDimensional weight calculator
