What Does the U Mean in Server Racks? Rack Unit Definition Explained

If you are new to server racks, you have probably seen terms like “1U switch” or “2U server” and wondered: what does the U mean in server racks? The answer is simple. A rack unit (often shortened to U or RU) is a standard measurement for the height of equipment that mounts in a server rack. One rack unit equals 1.75 inches or 44.45 millimeters.Today, the rack unit definition is universal. Any device labeled as 1U will fit into any standard 19-inch rack, regardless of the