In 1995 an ISO agreement was reached concerning container marking codes that would depict the length, height, and type of container in a short and easy-to-read sequence. This sequence is composed of four letters or digits. The first element of the sequence is about the length of the container, with the most common codes being 2 (20-foot container) and 4 (40-foot container). The second element is about the container height, with 2 (standard height of 8 feet and 6 inches) and 5 (high cube container of 9 feet and 6 inches) prevalent. The third and fourth refer to the container type. G1 relates to a general container with passive vents at the upper part of cargo space. R1 would be a mechanically refrigerated and heated container. U1 would be an open-top container with removable top members in end frames. P1 is a platform container with two complete and fixed ends. Finally, T1 is a tank container for non-dangerous liquids.
The most common container used for maritime shipping, a standard 40-footer, would have 42G1 as a sequence, while the same container as a high cube would have a sequence labeled as 45G1 (see above figure). 22U1 is a standard 20-foot open-top container. 45R1 is the most common sequence for a reefer (40-foot high cube). The container width code is usually not used since most containers have a width of 8 feet, but there are pools of containers with a width of 8 feet and 2 inches that use the E label. High cube 45-foot containers (LEG1) are convenient for intermodal transportation in Europe as they have a size that fits precisely 33 European pallets of 1.2 by 0.8 meters.