A rack unit, abbreviated as U (or RU), is a standardized unit of measurement used to describe the vertical space occupied by equipment in a server rack. This standardization allows IT equipment like servers, switches, routers, and patch. The U space of cabinets is an important concept for people working on IT infrastructure, data centers, or managing networks. Whether you are an expert or just a beginner in the field, it can still be challenging to figure out the U sizes—from small 6U cabinets up to giant 48U ones—without proper. U (rack unit, RU) is a unit of equipment height in a 19" rack. This article explains definition, planning, installation tips, and trends. The letter “U” stands for something called a rack unit. A server rack also helps optimize space.