Since the width of the rack’s mounting rails and the rack equipment itself is standardized, that part is simple—just make sure your equipment and your rack both follow the EIA-310-E standard. But you also need to consider the external width of the rack. The standard width for rack enclosures is 24 inches or 600 mm, which corresponds to the standard for removable floor tiles in a raised-floor data center. Extra-wide rack enclosures (31.5 inches or 800 mm) are also available, with or without extra depth.
Enclosures with extra width have side channels that accommodate PDUs, high-density cabling and cable managers without obstructing airflow. This is especially helpful for network switches that have side-to-side airflow and forward-facing ports. Extra-wide rack enclosures may also have modified vertical mounting rails that include built-in cable channels. Some extra-wide racks can even be customized with extra rack spaces at the sides to fit as much equipment as possible.