Each shipper uses a number called the DIM factor to calculate a package’s dimensional weight. To determine the DIM weight, you’ll take the volume and divide it by the DIM factor.
UPS, FedEx, and USPS each set their own DIM factor. These companies update their DIM factors every year. In 2019, the US Postal Service changed its DIM weight pricing model to apply to all packages greater than 1,728 cubic inches. DIM weight pricing doesn’t apply to USPS flat rate shipments.