Payload
Payload is the maximum permitted mass (or weight) of payload, including the dunnage and cargo securement arrangements that are not associated with the container in its normal operating condition. Therefore, Payload = Rating - Tare Mass.
If the tare mass of a 20' dry cargo container is 2,400 kgs. and a 40' is 3,900 kgs., the payload of 20' is 21,600 kgs. (i.e., 24,000 kgs. minus 2,400 kgs.) and 40' is 26,580 kgs. (i.e., 30,480 kgs. minus 3,900 kgs.). However, the exporter may be prohibited to have that much payload in areas where there are legal limitations to the overall load of a vehicle.
In exporting, it is common to encounter a payload of 17,500 kgs. or less in the 20' container, and 24,000 kgs. or less in the 40' container.