Dimensional or DIM weight pricing is a formula that carriers use to determine the cost to ship a package based on its volume. Dimensional weight pricing allows carriers to incorporate the size of the packages they ship into their pricing structure. After all, the number of packages that can fit on one truck or in one container depends as much on the size of the box as its weight.

Prior to 2015, the cost to ship a parcel was based on a very simple formula. Carriers used a table that would assign a base shipping rate for every combination of weight (1-150 lbs.) and zone (distance to be shipped). The heavier the package and/or the further it needed to travel, the more it cost to ship. This formula makes perfect sense until you think about one other factor: the fixed amount of space available in their trucks and aircraft. In 2015 FedEx, USPS, and UPS introduced a new pricing model called Dimensional Weight.