Considerations for Determining Rack Size
A rack unit, also known as “U”, “RU”, or “RMU”, was created by the Electronic Industries Alliance (EIA); it is the standardized unit of measurement in IT rack enclosures. 1U rack unit refers to 1.75 inches or 44.45 mm of vertical space. The most common rack sizes are 42U & 45U, and for high density equipment you can find racks up to 47U & 52U.