Carriers bill the greater of a package's actual weight and its dimensional weight: length × width × height in inches divided by a divisor, commonly 139 for UPS and FedEx daily rates. USPS applies dimensional weight to larger parcels using a divisor of 166. A box just 2 inches too big on each side can add pounds of billable weight, so right-sizing boxes is often the cheapest saving available.
Light, bulky products often cost more to ship by size than by weight. Dimensional (DIM) weight is how carriers charge for space in the truck.
The formula
DIM weight = (L × W × H) ÷ divisor. Billable weight = the greater of actual weight and DIM weight.
| Box | Cubic inches | DIM weight at 139 | DIM weight at 166 |
|---|---|---|---|
| 10 × 8 × 6 | 480 | 3.5 lb, billed 4 | 2.9 lb, billed 3 |
| 12 × 10 × 8 | 960 | 6.9 lb, billed 7 | 5.8 lb, billed 6 |
| 14 × 12 × 10 | 1,680 | 12.1 lb, billed 13 | 10.1 lb, billed 11 |
| 16 × 12 × 12 | 2,304 | 16.6 lb, billed 17 | 13.9 lb, billed 14 |
Carriers round dimensions and weights up. Check current rules and your negotiated divisor before relying on these numbers.
How to lower billable weight
- Use the smallest box that protects the product with about 1 to 2 inches of padding.
- Stock several box sizes rather than one that fits everything.
- Use a poly or padded mailer for soft or unbreakable items.
- Consider custom dimensions when volume justifies the minimum order.
Box strength
| Rating | Measures | Common single-wall grade |
|---|---|---|
| ECT (edge crush test) | Stacking strength | 32 ECT |
| Burst (Mullen) test | Puncture and burst resistance | 200 lb test |
Heavy or fragile items may need 44 ECT or double-wall boxes. The rating is printed on the box maker’s certificate on the bottom flap.
Add the box to your cost per shipment. Browse packaging.
Common questions
How do I calculate dimensional weight?
Multiply length, width and height in inches, rounded per the carrier's rules, then divide by the carrier's divisor. Compare it to the actual weight and pay the higher.
What is the DIM divisor for UPS and FedEx?
139 for daily rates is the common published divisor. Negotiated contracts can differ, so check your account.
Does USPS charge dimensional weight?
For larger parcels, yes. USPS uses a divisor of 166 on packages over one cubic foot for most services. Check current USPS rules.
What does 32 ECT mean on a box?
It is the edge crush test rating, a measure of stacking strength. 32 ECT single-wall boxes are the common choice for parcels.