How to calculate dimensional weight
- Measure the length, width and height of the box at its longest points, including any bulges.
- Enter the dimensions and the actual weight, in inches and pounds or centimetres and kilograms.
- The table shows the dimensional weight and billable weight for common carriers. Billable weight is the higher of actual weight and dimensional weight, rounded up.
The formula
Dimensional weight = Length × Width × Height ÷ DIM divisor
| Carrier | Imperial divisor (in³/lb) | Metric divisor (cm³/kg) |
|---|---|---|
| UPS & FedEx (daily rates) | 139 | 5,000 |
| USPS (packages over 1 cubic foot) | 166 | ≈ 6,000 |
| DHL Express | 139 | 5,000 |
| Air cargo (IATA) | 166 | 6,000 |
| Amazon FBA (fee calculation) | 139 | 5,000 |
Example: a 16 × 12 × 8 inch box = 1,536 cubic inches. ÷ 139 = 11.05, so UPS and FedEx bill it as 12 lb even if it only weighs 5 lb.
Carriers may use different divisors for negotiated contracts, retail counters and specific services, and they round dimensions to the nearest whole inch first. Check your carrier’s current service guide.
Why carriers use dimensional weight
A truck or plane fills up by space as well as by weight. A large box of pillows takes up as much room as a box of books but weighs a fraction as much. Dimensional pricing makes sure light but bulky parcels pay for the space they use.
Dimensional weight and Amazon FBA
For most size tiers, Amazon uses the greater of unit weight and dimensional weight (L × W × H ÷ 139, with width and height treated as at least 2 inches) as the shipping weight that determines the FBA fulfillment fee. Shaving an inch off your packaging can drop the shipping weight into a lower band — run the numbers in our Amazon FBA Calculator.
How to reduce DIM weight charges
- Use the smallest box that protects the product; avoid shipping air.
- Use poly mailers for soft, non-fragile items.
- Redesign retail packaging to be more compact, or ship flat-pack where possible.
- Ask carriers about negotiated divisors if you ship in volume.
Frequently asked questions
What is the DIM divisor for UPS and FedEx?
139 cubic inches per pound for daily (account) rates. Divide L × W × H in inches by 139.
Does USPS use dimensional weight?
Yes, for packages larger than one cubic foot (1,728 cubic inches), using a divisor of 166.
How is billable weight calculated?
It is the greater of the actual weight and the dimensional weight, usually rounded up to the next whole pound or half-kilogram.
How do I convert to metric?
Measure in centimetres and divide L × W × H by 5,000 (express couriers) or 6,000 (air cargo) to get kilograms.