The rack unit size is based on a standard rack specification as defined in EIA-310. The Eurocard specifies a standard rack unit as the unit of height; it also defines a similar unit, horizontal pitch (HP), used to measure the width of rack-mounted equipment. The standard was adopted worldwide as IEC 60297 Mechanical structures for electronic equipment – Dimensions of mechanical str. 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. 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.