CBM is the short name of Cubic Meter, 1 CBM is (1 meter length x 1 meter width x 1 meter height ) = 1 cubic meter (CBM). CBM to use in transportation measeurment doesn't mean that the goods packaging must be 1 meter with single package. 1 cubic meter cargo can be one package, also can be many piece of packages accumulated.
We normally measure goods cubic meter one by one, carton, pallets, walve bag, air flight case, wooden crate, wooden case, some time accumulate the packages all togeter then measure it. but the datum are the same
Most goods with different angle, size, and geometrical dimension is diversity, so we normally measure its physical cubic.