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. This measurement helps in organizing and fitting various devices, such as servers, network switches, and storage units, into a rack system efficiently. Rack units are essential for ensuring that equipment fits properly within a data center or other environments where space is limited. By using rack units, technicians can easily determine how much space is available and how many devices can be installed, promoting better organization and airflow.