The IT industry uses 1U as a unit of measure to designate racks and rack-mounted equipment. U is the Electronic Industries Alliance (EIA) standard unit for specifying rack height. It denotes the vertical space available for a rack-mounted device. Racks, cabinet spaces, and the devices that fit in them are all measured in U. 1U refers to a height of 1.75 inches or 4.445 cm. This is the space between the rack shelves that is available for device installation. The size of rack mountable devices are often specified in U with a number. A one-rack device is a 1U, while a 2U device requires two rack units. Rack-mountable hardware is manufactured according to the number of total U’s, or rack units, that the equipment will require in the data rack.
1U Rackmount Devices
Devices are manufactured to allow for small amounts of space around equipment following installation. 1U rackmount devices fit a 1.75-inch vertical space. However, their actual height will be less, at around 1.72 inches. A 2U device will have an actual height of just under 3.5 inches to comply with available rack space, plus ease of installs and removals. Server systems, switches, and other devices are built to work with rack dimensions. A full size rack is 42U, while a half-height rack is 18 to 22U.
Rack Units Measure Vertical Space
The U measurement of vertical rack space may be called a rack unit, abbreviated as RU. It is used to physically describe the racks themselves and the devices they accommodate. For example, a 30U rack will provide 30 rack units, while a 3U device will occupy three units of rack or chassis space. Comms Express can explain how exact dimensions should be considered when buying racks.