What Is Dimensional Weight?
Dimensional weight (also called DIM weight or volumetric weight) is a pricing technique that accounts for the space a package occupies in a delivery vehicle — not just how heavy it is. Carriers introduced DIM weight because a large, light box takes up the same cargo space as a small, heavy one, but under actual-weight-only pricing, the light box would be far cheaper to ship.
The result: if you ship something like a bag of foam peanuts, a large empty frame, or a lightweight shoe box, you are almost certainly paying for more weight than your scale shows.
The DIM Weight Formula
The formula is straightforward:
DIM Weight = (Length × Width × Height) ÷ DIM Divisor
Dimensions are measured in inches (for US carriers using imperial) or centimeters (for international shipments). The divisor is set by each carrier:
| Carrier | Domestic Divisor (inches) | International Divisor |
|---|---|---|
| UPS | 139 | 139 |
| FedEx | 139 | 139 |
| DHL (US domestic) | 139 | 5,000 (cm³/kg) |
| USPS Priority Mail | 166 | 166 |
For UPS/FedEx domestic: DIM weight (lbs) = (L" × W" × H") ÷ 139
When Does DIM Weight Apply?
For UPS and FedEx, DIM weight always applies to all packages — the carrier charges whichever is greater: actual weight or DIM weight. There is no minimum size threshold.
For USPS, DIM weight only applies to Priority Mail and Priority Mail Express packages larger than 1 cubic foot (1,728 cubic inches).
A Real Example
You ship a package of lightweight holiday decorations:
- Actual weight: 3 lbs
- Dimensions: 18" × 14" × 12"
- DIM weight: (18 × 14 × 12) ÷ 139 = 3,024 ÷ 139 = 21.8 lbs → billed as 22 lbs
You're paying for 22 lbs instead of 3 lbs — more than 7× the rate you might have expected. On a UPS Ground rate, that difference could be $15–$40 more per package.
How to Optimize Your Packaging
Reducing box size is the single most effective way to cut DIM weight charges:
- Use the smallest appropriate box — leave just enough room for padding, nothing more
- Use lightweight void fill — air pillows instead of foam peanuts save actual weight too
- Custom packaging — if you ship high volumes of the same product, a custom box cut to exact dimensions can reduce DIM weight significantly
- Flat-rate options — for heavy-for-size items, USPS Priority Mail Flat Rate boxes charge a flat fee regardless of weight (up to 70 lbs), potentially reversing the DIM weight penalty
Even reducing a box from 18×14×12 to 16×12×10 drops DIM weight from 22 lbs to 14 lbs — an 8-lb savings per shipment that adds up quickly at volume. Use our shipping calculator to compare rates for different package dimensions.