Height unit

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Height units of different devices in the rack
Dimensions of height units

A height unit ( English unit , short U or rack unit , short RU ), short HE , is a unit of measurement used for electronics housing ( English rack ) to describe the height of the device. Devices with one height unit are referred to as "1U" (or "1U"), devices with two height units as "2U" etc.

1 U corresponds to 1¾ inch , i.e. 44.45 millimeters .

Device housings that are dimensioned according to HE are intended for installation in so-called 19 ″ racks. The width of the 19 "front panels is 482.6 mm, the distance between the mounting screws is 18 5/16 inches, or 465.14 mm. Since this dimension is often not exactly adhered to in the rack, the front panels of many devices have mounting slots instead of holes so that they can be safely installed with tolerance.

Often a server with a height of 1U is jokingly referred to as a pizza box because of the resulting housing shape .


The HE is of particular importance in data centers . There the computers are often operated in 19 ″ racks with a limited height, and when a device is housed ( server housing ), you pay for the required height units, among other things.

Furthermore, HE are also used in the field of sound and event technology as a measure of the height of technical devices. Almost the entire signal chain can be accommodated here in 19 "racks, from the mixer to the power amplifier .

Further applications can be found in telecommunication systems, radio technology, measuring devices, in control and regulation technology and in medical technology.

See also

Individual evidence

  1. Define: Rack Unit “U” or “RU”. In: The Server Rack FAQ - Information about rack issues and racking servers. Retrieved October 30, 2019 (American English).
  2. Define: EIA-310. In: The Server Rack FAQ. Retrieved October 30, 2019 (American English).