How volumetric weight works
Carriers bill the larger of two numbers: the actual weight on the scale, or the volumetric (DIM) weight derived from the box's length × width × height divided by a carrier-specific factor. Oversized but light parcels are normally billed by volume.
Why carriers use dimensional weight
A large, light box takes up trailer space that could fit several dense parcels. Converting dimensions to an equivalent weight lets carriers bill fairly for that space. The calculator uses each carrier's published divisor.