The rack density describes the height of a unit. The standard height of one unit is 1.75 inches, so rack density is described in terms of the number of units, such as one unit (1U), 2U and so on. Blade servers are noted as “number of blades per blade chassis/height” (in standard U height), so 14 blades per blade chassis height of 7U would be listed as “14/7U.”