Dimensional Weight (DIM):

 

Dimensional (DIM) weight refers to how dense a package is, or the amount of space a package occupies relative to its actual weight. The classic example of a low-weight, high-volume shipment is a box of ping-pong balls — they occupy a disproportionate amount of space relative to their weight. Parcel carriers use DIM weight to ensure fair payment for shipping parcels that are relatively light for their size.

The actual billable weight of a parcel becomes the greater of the dimensional weight or the actual weight. The dimensional weight is calculated by dividing the cubic size of a parcel in inches (the product of multiplying your package's length x width x height) by a factor provided by the parcel carrier (subject to change).