In reference to product rack height, a unit is a universal measurement: 1.75 inches or 44 mm. 1U (Unit) high refers to 1.75 inches, 2U high refers to 3.5 inches, etc.

A rack unit is a measurement of height equal to 1.75". Additionally, the mountable area of a standard rack is 19" wide with holes pre-drilled so as to allow standard gear to be placed in only full rack unit increments. Rack depths vary. Rack mountable gear has mounting "ears" that bring the width of the unit to 19", height being measured in rack units, or RU's. While most patchbays are available in 1RU and 2RU configurations, Bittree has originated a 1.5RU panel, mountable in 1/2RU increments, allowing the use of full size designation strips on a panel less than 2RU.

1 Rack Unit (RU or U), is defined as a height of 44.5 mm. When purchasing equipment for mounting in a rack, the height is often specified in RU. This is a convenient way for you to ensure that the correct height of rack is bought to house your equipment.