Shipping Box Fitment Optimizer

Parcel carriers price on space as well as mass, because a delivery van fills up by volume long before it reaches its weight limit. Dimensional weight converts a box's volume into an equivalent weight by dividing cubic inches by a divisor, 139 for current UPS and FedEx domestic daily rates and 166 under several retail and USPS schemes, and the shipper pays on whichever is larger, the scale weight or the dimensional weight. That divisor is really a density threshold. Since a cubic foot is 1,728 cubic inches, a divisor of 139 means any package lighter than about 12.4 pounds per cubic foot is billed on its size rather than its weight, while a divisor of 166 lowers that break-even to about 10.4 pounds per cubic foot. Anything below the threshold is, for pricing purposes, shipping air. This is why padding is expensive. Adding two inches of cushioning on every side adds four inches to each axis, and volume grows with the product of three inflated edges: a 12 by 8 by 6 inch item occupies 576 cubic inches, but the 16 by 12 by 10 inch void it needs is 1,920 cubic inches, more than triple, with a dimensional weight near 13.8 pounds regardless of what the item actually weighs. Protection still has to come first; roughly one to two inches of cushioning suits ordinary goods and two to three inches suits fragile items, with the practical test being that the contents cannot shift or touch a wall when the sealed box is shaken. Note the limits of this comparison. It searches a fixed list of twelve common box sizes and allows the item to be rotated but not placed diagonally, carriers round each measured dimension up to the next whole inch and measure the outside of the box, so corrugated wall thickness pushes real outer dimensions past nominal inner ones, and large negotiated accounts often carry a divisor other than 139.

The corrugated shipping box itself is a nineteenth century invention. Albert Jones of New York patented pleated, corrugated paper as a wrapping material in 1871, and Robert Gair of Brooklyn developed machinery that cut and creased paperboard into pre-formed folding cartons in the 1870s and 1880s, which made mass-produced boxes cheap. American railroads accepted corrugated containers in place of wooden crates in the early twentieth century, and the regular slotted container became the default style still used for nearly all parcels today. Pricing by volume came from aviation, where payload space is the scarcest resource. The International Air Transport Association standardized volumetric weight for air cargo and, effective 1 January 2015, tightened its general divisor from 6,000 to 5,000 cubic centimeters per kilogram. Ground parcel carriers moved the same direction as e-commerce filled their networks with light, bulky cartons. UPS and FedEx had long applied dimensional weight only to ground packages above three cubic feet, but both announced in 2014 that from the end of December 2014 and the start of 2015 the rule would apply to every ground package regardless of size. In January 2017 both carriers cut the domestic divisor from 166 to 139, roughly a 19 percent increase in the billable weight of any volume-billed parcel. Right-sizing boxes, once a materials-cost question, became a freight-cost question at that point, and automated box-selection and on-demand box-making equipment spread through fulfillment centers in the years that followed.