Enter a box size and its real weight. This shows the dimensional weight, the billable weight the carrier charges on, and how much air you are paying to ship.
Carriers bill on whichever is greater, the real weight of the box or its dimensional weight. Enter the box and pick the divisor that matches your rates.
UPS publishes 139 for daily rates and 166 for retail rates. USPS moved from 166 to 139 on 12 July 2026, rounds every fractional dimension up to the next whole inch, and applies dimensional weight only to packages over 1,728 cubic inches. FedEx publishes its divisor in its annual service guide, so use the custom option with the number in your own agreement.
Trucks and planes run out of space before they run out of weight. A box of pillows takes the same room as a box of bolts and earns the carrier far less. Dimensional weight is how carriers charge for that space. They convert the size of your box into a weight and bill you on it when it comes out heavier than the scale does.
This is why a light product in an oversized box costs more to ship than the same product in a box that fits it. The scale says two pounds. The carrier says nine.
Multiply length by width by height to get the cubic size of the box. Divide that by the carrier's divisor. Round the answer up to the next whole pound. That is the dimensional weight. Compare it to the real weight and the higher number is what you pay on.
(Length × Width × Height) ÷ Divisor = Dimensional weight
A smaller divisor produces a bigger billable weight. Moving from 166 to 139 raises the dimensional weight on the same box by about 19 percent.
| Carrier and rate type | Divisor | Notes |
|---|---|---|
| UPS daily rates | 139 | Applies with a scheduled pickup or an account with daily rates |
| UPS retail rates | 166 | Applies at a UPS location or without an account |
| USPS, from 12 July 2026 | 139 | Only on packages over 1,728 cubic inches. Dimensions round up to the whole inch |
| USPS, before 12 July 2026 | 166 | The old number, useful for checking older invoices |
| FedEx | See your agreement | Published in the annual FedEx service guide. Use the custom option above |
Most brands lose money here without seeing it. Packaging gets chosen for how it looks or what is already in the stockroom, then every order ships in a box with several inches of air in it. The cost shows up on the carrier invoice weeks later as a weight nobody recognises.
Two things fix it. Pack to the product rather than to the shelf, and price every label across more than one carrier, because the divisor is only one of the numbers that moves. At BoxHero every order is rate shopped across the carriers we run, and the cheapest service that still hits the delivery date wins.
No. You are charged on whichever is greater. Dense items usually bill at their real weight. Light and bulky items usually bill at dimensional weight.
It depends on the carrier. USPS applies it only above 1,728 cubic inches, which is one cubic foot. UPS publishes no size floor and states that it can apply to its domestic and international package services.
Round up. UPS states that measurements round up to the next whole number, and USPS began rounding every fractional dimension up on 12 July 2026. Measure the outside of the packed box, including any bulge.
Use a smaller box. Cubic size is the only input you control, and it moves fast, because shaving an inch off all three sides of a 12 inch cube cuts the cubic size by about a quarter.
Shipping by pallet instead? The freight class calculator works out density and class, and the pallet configuration calculator shows how many cartons fit. All our tools are on the shipping calculators page.
Tell us your orders a month and units per order. You see a per-order price before you commit to anything.
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