What is a TEU?

TEU stands for twenty-foot equivalent unit, the standard measure of container capacity. One TEU represents one standard twenty-foot ISO container, so it is a common scale for counting boxes of different lengths: a forty-foot container, by far the most common box in deep-sea service, counts as two TEU, and a forty-five-foot high-cube is also normally counted as two TEU. Height does not change the count; standard and high-cube boxes of the same length are the same number of TEU.

The unit lets one number describe very different ships and flows. A container ship's capacity is quoted in TEU, from small feeders of a few hundred TEU, through the workhorse sizes in the thousands, up to ultra-large container vessels above 24,000 TEU. Ports and terminals report annual throughput in TEU, liner operators are ranked by total fleet TEU capacity, and trade statistics use it to compare volumes between routes and years.

Two practical caveats stop TEU being misread. First, it measures slots, not weight. A standard twenty-foot box has a maximum gross mass of roughly 30 tonnes, and if every slot were filled to that limit the ship would exceed its deadweight long before it ran out of slots, so a ship is limited by TEU capacity and deadweight together; nominal TEU assumes a fairly light average box weight, and the achievable loaded count on a heavy cargo mix is lower. Second, not all slots are equal: reefer containers need powered slots, stack weight and lashing limits restrict where heavy boxes can go, and visibility and stability constraints shave the practical number further. Planners therefore distinguish nominal capacity from what the ship actually lifts in service.

For quick orientation: when you read that a carrier operates three million TEU, that is fleet slot capacity, not boxes moved; when a port claims ten million TEU a year, that is throughput, with each box counted at each handling. Keeping those senses of the unit apart, and remembering the weight limitation, is most of what a professional needs to know about the term.