This "half rack width" concept is popular in applications where IT equipment is being used by military who are unable to use traditional 1U full-depth IT appliances due to their large size.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.