units measuring 9 feet 6 inches (2.90 m) have become very common in recent years. By the end of 2013, high-cube 40 ft containers regression represented almost 50 of the worlds maritime container fleet, according to Drewrys Container Census report.[37] About 90 of the worlds containers regression are either nominal 20-foot (6.1 m) or 40-foot (12.2 m) long,[4][38] although the United States and Canada also use longer units of 45 ft (13.7 m), 48 ft (14.6 m) and 53 ft (16.15 m). ISO containers regression have castings with openings for twistlock fasteners at each of the eight corners, to allow gripping the box from above, below, or the side, and they can be stacked up to ten units high.[39][nb 8] Regional intermodal containers regression, such as European and U.S. domestic units however, are mainly transported by road and rail, and can frequently only be stacked up to three laden units high.[39] Although the two ends are quite rigid, containers regression flex somewhat during transport.[43] Container capacity is often expressed in twenty-foot equivalent units (TEU, or sometimes teu). A twenty-foot equivalent unit is a measure of containerized cargo capacity equal to one standard 20-foot (6.1 m) long container. This is an approximate measure, wherein the height of the box is not considered. For example, the 9 ft 6 in (2.9 m) tall high-cube, as well as 4-foot-3-inch (1.3 m) half-height 20-foot (6.1 m) containers regression are equally counted as one TEU. Similarly, extra long 45 ft (13.72 m) containers regression are commonly designated as two TEU, no different than standard 40 feet (12.19 m) long units. Two TEU are equivalent to one forty-foot equivalent unit (FEU).[44][45] In 2014 the global container fleet grew to a volume of 36.6 million TEU, based on Drewry Shipping Consultants Container Census.[46][nb 9] Moreover, in 2014 for the first time in history 40-foot High cube containers regression accounted for the majority of boxes in service, measured in TEU.