It can also describe a unit that is 1U high and half the depth of a 4-post rack (such as a network switch, router, KVM switch, or server), such that two units can be mounted in 1U of space (one mounted at the front of the rack and one at the rear).OverviewA rack unit (abbreviated U or RU) is a unit of measure defined as 1+3⁄4 inches (44.45 mm). It is most frequently used as a measurement of the overall height of, as well as the height of eq. The rack unit size is based on a standard rack specification as defined in -310. The specifies a standard rack unit as the unit of height; it also defines a similar unit, (HP), used to measure the width o. A typical full-size rack is 42U, which means it holds just over 6 feet (180 cm) of equipment, and a typical "half-height" rack is 18U–22U, which is around 3 feet (91 cm) high. The mounti.