There are approximately 1,200 cubic feet in a 20-foot container. Measurement varies slightly and depends on the contents, type and exact capacity of the container.
The cubic foot measurement for containers used for intermodal shipping were standardized in the 1960s. Typical containers of the time were either 20 feet or 40 feet, and as such, the International Organization for Standardization developed the 20-foot equivalent unit, or TEU, to describe capacity. For example, the capacity of one 20-foot container is equal to one TEU.
The cubic foot measurement of a 20-foot container is typically near 1,170 but can be as large as 1,520. The figure fluctuates depending on length, width, and internal capacity of the container.