Understanding Rack Units
One rack unit, or 1U, equals 1.75 inches (44.45 mm). Common rack heights are 42U, 45U, and 48U. Switches and patch panels are often 1U, many servers are 2U, larger storage and blade systems use 3U or more, and UPS systems can exceed 10U. Place heavy equipment low, reserve cable-management space, account for airflow, and group related equipment.