Is there a standard unit of measure for freight? How do airlines measure the "load factor"? I am aware that is more complex than the passenger measures. Freight is a mix of weight and volume. eg you can send a plane out packed to the ceiling with cut flowers, but the maximum payload would not be reached as flowers weigh so little. In terms of measuring this, one can say that the plane is going out 100% full by the volume measure, but it is only going out 50% full if the unit of measure is weight. (Please note, the 50% is a theoretical number only).

I'd like to learn more about how airlines measure this side of their operations. Thanks in advance for your help.