A 12U rack or cabinet can house equipment whose total height when placed into the rack is no more than 0. Houses network switches and patch panels up to 20. SmartRack 12U Low-Profile Switch-Depth. 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. Among the most used rack sizes are 9U, 12U and 18U, each designed to cater to specific space and capacity requirements. Understanding these rack sizes is essential for IT professionals, as they influence not only the physical layout of server rooms but also the overall performance and scalability. Packaging: 720 x 735 x 840 mm (28. 1") Rack: 600 x 720 x 650 mm (23.