Dimensional weight is the standard measure for large carriers now. The changeover at UPS started way back in 2007. UPS does it, FedEx does it, and USPS does it for certain classes of packages. You can thank large shippers like Amazon that often put a tiny product in to a huge box with a bunch of air bags: weight alone doesn't capture the fact that fewer of these boxes can be shipped per truck/flight than if it were packaged more efficiently.