Dimensional weight, in one minute
Carriers price a parcel on the space it occupies, not just its scale weight, because a light, bulky box fills a truck before it fills the weight limit. They convert size into an equivalent weight — the dimensional weight (DIM weight) — and bill on whichever is larger.
DIM weight = (L × W × H in inches) ÷ divisor → round up to the next whole pound
Billable weight = the greater of (actual weight, DIM weight), minimum 1 lb
The divisor by carrier
| Carrier | Divisor (in³/lb) | Notes |
|---|---|---|
| UPS | 139 | All packages; rounds each dimension up since Aug 2025 |
| FedEx | 139 | All packages; rounds each dimension up since Aug 2025 |
| USPS | 166 | Priority / Priority Express only, and only above 1 cubic foot |
| DHL | 139 | Applies to all shipments (5000 in cm/kg) |
A larger divisor gives a smaller DIM weight, which is why high-volume shippers negotiate divisors above 139 in their contracts. If you have a negotiated rate, choose Custom above and enter your number.
The 2025 rounding change
Effective August 18, 2025, UPS and FedEx round every fractional inch up before calculating cubic size. A box measured at 11.1 × 8.5 × 6.2 inches is now treated as 12 × 9 × 7. That inflates the volume and can add a pound or more to the billable weight — and can tip a parcel into Additional Handling territory. This calculator applies that rounding by default for UPS and FedEx; you can turn it off to see the un-rounded figure.
The USPS exception
USPS is the outlier: it applies dimensional weight only to Priority Mail and Priority Mail Express packages larger than one cubic foot (1,728 cubic inches). Anything at or below 1 cubic foot — and services like Ground Advantage — is billed on actual weight alone. Select USPS and the calculator checks the cubic-foot threshold for you and tells you which rule applied.
A worked example
A box of cushions, 20 × 16 × 10 inches, actual weight 7 lb, shipping UPS Ground:
- Cubic size: 20 × 16 × 10 = 3,200 in³
- DIM weight: 3,200 ÷ 139 = 23.02 → 24 lb (rounded up to the next whole pound)
- Actual weight: 7 lb
- Billable weight: the greater = 24 lb
You pay for 24 lb, not 7 — the box is light for its size. Drop the longest side to 18 inches and the DIM weight falls to 2,880 ÷ 139 = 20.72 → 21 lb. Small dimension changes move real money at volume.
Cutting your billable weight
- Right-size to whole-inch dimensions so the ceiling rounding doesn't cost you a phantom inch.
- Use the smallest box that protects the product; remove excess void fill.
- Stay clear of the 1-cubic-foot line on USPS Priority if actual weight is low.
- If you ship volume, ask your account rep about a higher negotiated divisor.