You'll get the precise, standardized physical dimensions of a 1U rack unit — 1. 45 mm) in height and 19 inches (482. 794 for calculating in millimeters. This gap allows a bit of. A rack unit (abbreviated U or RU) is a unit of measure defined as 13⁄4 inches (44. 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. dimensions, mounting interf th a typical depth r structural topology accommodates (hot-swappable AC/DC l cycling.