A "rack unit" (often abbreviated as "U") is a standard measurement used to describe the height of equipment that can be mounted in a server rack. One rack unit is equivalent to 1.75 inches (44.45 mm) in height. Equipment such as servers, switches, and routers are designed to fit within these standardized dimensions, allowing for efficient organization and space management in data centers. Rack units help ensure compatibility among various devices and make it easier to plan the layout of a data center. For example, a device that is 3U tall will take up three rack units of space. This standardization simplifies installation and maintenance of equipment in a rack-mounted system.