How the calculation works
The calculator rounds each outside dimension to the nearest whole inch, multiplies length × width × height, divides the cubic volume by the selected DIM divisor, and rounds the result up to a whole pound. It then compares that result with rounded actual weight. The larger number is the estimated billable weight.
FedEx publishes a divisor of 139 for U.S. shipments. UPS lists 139 for Daily Rates and 166 for Retail Rates. USPS applies its published domestic DIM rule only when the package exceeds 1,728 cubic inches for Priority Mail Express, Priority Mail, USPS Ground Advantage and Parcel Select shipments to zones 1–9.
Why a smaller box can change the invoice
A lightweight product in an oversized carton may be billed as though it weighs several times more than it does. Measure the finished, sealed package—not the product or internal carton. Compare the result before changing materials: reducing empty space can lower DIM weight, but protection and damage rates still matter.
For a deeper workflow, read our guide to reducing dimensional-weight costs without increasing damage.
Primary carrier sources
- FedEx: What is dimensional weight?
- UPS: Shipping dimensions and weight
- USPS: Postage verification and dimensional weight
Important limitation
This is an educational estimate, not a carrier quote. Contract terms and service-specific rules can differ, and additional-handling or oversize charges may apply independently of DIM weight. Confirm final billing rules with your carrier or shipping platform.