What is the size of a 42U server rack?

The U measurement is that of the internal height available for equipment to be housed. For this size server the internal height is 42U. The overall height of the cabinet (measured in mm or cm or metres) will be bigger than this, to take into account the top and bottom of the rack and any castors or feet fitted to the cabinet. The U-measurement is for height only. The width and depth are typically measured in millimetres (mm).