What is Rack Unit?
A Rack Unit, expressed as U or RU is a unit of measure, which describes the height of electronic equipment designed to mount in a 19- inch rack or 23- inch rack of the server. The 19 inches (482.60mm) or 23 inches (584.20 mm) specification represents the width of the equipment mounting frame in the rack. It incorporates the width of the equipment that can be mounted inside the rack is less.
One rack unit can be expressed as 1.75 inches (44.45 mm) high. A 19 inch wide racks are commonly preferred in computer equipment, which is usually 17.25″ (438mm) wide. The height of the rack- mounted equipment is denominated as “U”. For example, 1 Rack Unit is often described as “1U”, 2 rack units as “2U” and so on.