Dimensional weight or volumetric weight is a technique to calculate the shipping cost for commercial freight transport. It is mainly used by postal and courier service providers to consider both weight and volume of the packaging to determine appropriate shipping cost.
Until 2015, even companies like UPS and FedEx charged for shipping based on the weight. They applied the dimensional weight matrices only on a specific size range of the package. But, shipping large sized, lightweight packages would cut their profits. Hence, most shipping companies globally decided to use dimensional weight to calculate their freight charges.
Dimensional weight is the theoretical weight of the package. The calculation varies depending on the shipping company and types of shipment. It is the weight of the package at a given minimum density as determined by the freight carrier. For example, if a carrier has stated- one cubic foot package has a minimum allowance of 10 pounds and your one cubic foot package weighs 9 pounds, you will be billed for 10 pounds. If it weighs 12 pounds, then it will be billed for 12 pounds.
To calculate the dimensional weight, you need to know the DIM Factor (dimensional weight factor). The DIM Factor is the allowed volume per unit weight. Therefore, it is expressed in cubic inches/lbs. or cubic feet/lbs. or as cubic meters/kg. You can calculate the dimensional weight of your package by dividing its volume by DIM factor. If your package is non-cubical, then its volume would be the volume of the smallest cuboidal package, which could fit it completely. You need to be careful while using the measurement units. Most US shipping companies use the imperial system (pound, inch, etc) whereas the rest of the world uses the metric system (kilogram, centimeter). The DIM factor also varies according to domestic or international shipment. For example, UPS uses a DIM factor of 166 for domestic packages with a volume equal to or lower than 1,728 cubic inches. Its DIM factor is 139 for any package with greater volume than above. For US Export and Import, UPS uses 139 DIM Factor 139.
Dimensional weight can be expensive for shipping lightweight parcels. For example, items like books, documents, optical discs, fabrics, pillows, stuffed toys, etc may cost higher than regular shipping charges. However, most soft products can be compressed to occupy a smaller space or vacuum packed. You can pack books, discs, and documents in flat packaging such as paperboard or plastic envelopes. You can also cut down the shipping charges by using the right padding and void fills.