The twenty-foot equivalent unit (abbreviated TEU or teu) is a unit of measurement used to describe the cargo-carrying capacity of container ships and container ports. It is based on the volume of a standard 20-foot intermodal container, which is a metal box that can be easily transferred between different modes of transportation. The length of the container is standardized, but the height can vary between 4 feet 3 inches and 9 feet 6 inches, with the most common height being 8 feet 6 inches.

One TEU is equivalent to the volume of a 20-foot container, and a 45-foot container is commonly referred to as 2 TEU, rather than 2.25 TEU. This unit of measurement is commonly used in the shipping industry to describe the capacity of a container ship or port. It is an inexact unit, as the actual volume of a container can vary depending on its height and other factors.