Glossary · Racks & Power
U (Rack Unit)
A rack unit ("U") is 1.75 inches (44.45 mm) of vertical space in a 19-inch rack — the measure that sizes everything mounted in one. A switch is often 1U, a NAS 2U, a UPS 1–2U. Rack depth and U-count are how homelabbers plan a build before buying a frame.
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