Shipments are measured in Gross Volume and Gross Weight, where volume is measured in Cubic Meters (CBM) and Weight in Kilograms (KG). 

(CBM can be determined through multiplying length, width, and height in meters.)

Freight forwarders will generally charge Less Container Load (LCL) rates in terms of per CBM.

But all shipments will be required to have the CBM and KG, regardless of container

Generally a 20ft container will hold 27.9 CBM and 2930 KG and a 40ft will hold 56.1 CMB and 3900 KG.