Originally defined by the EIA-310 standard, the rack specifies a front panel width of 19 inches (482. 6 mm), allowing different hardware from various manufacturers to fit in the same enclosure. Common server rack sizes are 19‑inch width, heights like 42U or 48U, and depths from ~24″ to 48″. Most IT environments default to 42U, 19-inch width, and 1000–1200 mm depth unless space constraints or special equipment dictate. A 19-inch rack is a globally standardized frame used for mounting servers, network equipment, industrial controls, and audiovisual equipment. Height is measured in rack units (U). Width is usually 19 inches inside, which is the space for. 1. The size of a system can total from a dozen up to a hundred of active.