Rack unit

A rack unit (abbreviated U or RU) is a unit of measure defined as 1+3⁄4 inches (44.45 mm).^[1]^[2] It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby the height of the frame or equipment is expressed as multiples of rack units. For example, a typical full-size rack cage is 42U high, while equipment is typically 1U, 2U, 3U, or 4U high.

^ IEC 60297-3-108:2014. Mechanical structures for electronic equipment - Dimensions of mechanical structures of the 482,6 mm (19 in) series - Part 3-108: Dimensions of R-type subracks and plug-in units, International Electrotechnical Commission
^ West, Jill; Dean, Tamara; Andrews, Jean (2015). "Structured Cabling and Networking Elements". Network+ Guide to Networks (Seventh ed.). Boston, MA: Engage Learning. p. 169. ISBN 9781305480865. Retrieved 9 December 2019. Racks are measured in rack units (RU or U) with the industry standard being 42U tall — about 6 feet.

[1] IEC 60297-3-108:2014. Mechanical structures for electronic equipment - Dimensions of mechanical structures of the 482,6 mm (19 in) series - Part 3-108: Dimensions of R-type subracks and plug-in units, International Electrotechnical Commission

[2] West, Jill; Dean, Tamara; Andrews, Jean (2015). "Structured Cabling and Networking Elements". Network+ Guide to Networks (Seventh ed.). Boston, MA: Engage Learning. p. 169. ISBN 9781305480865. Retrieved 9 December 2019. Racks are measured in rack units (RU or U) with the industry standard being 42U tall — about 6 feet.

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