U

Abbreviation for the “modular Unit” on which rack panel heights are based. According to EIA and ANSI standards one modular rack unit (1U) is 1.75″ tall (that’s 44.25 millimeters for those of you in the rest of the world). Accordingly 2U would be 3.5″ tall, and so on. These modular units are also referred to as rack units or rack spaces. The holes in a standard rack rail are spaced according to these specs and most of the rack mountable equipment we use is designed to occupy a fixed number of rack spaces (1U, 2U, 3U, etc.)