USPS has been using volumetric weight since 2007. They call it shape-based postal pricing
For the Global Express Guaranteed shipping option, USPS applies the International Air Transport Association (IATA) standard DIM factor of 166 cu in/lb (or 6000 cm3/kg for the metric system).
When shipping domestically through Priority Mail to Zones
5–9, put 194 cu in/lb (7000 cm3/kg) into the dimensional weight formula. USPS uses DIM weight only for parcels over 1 cubic foot/1,728 cu in.
There is no USPS dimensional weight calculator online — estimate it manually or set up Calcurates
to automate the routine.