Rack Unit Calculator
Plan rack space in seconds: enter your device mix, pick a rack size, and see used units, free units, and the physical height — with U-to-inches and millimeters conversion built in.
Used
30U
Free
12U
Height (in)
52.50"
Height (mm)
1334
1U = 1.75 inches = 44.45 mm. Remember to reserve space for switches, PDUs, cable management, and blanking panels.
Space Is Rarely What Fills First
A 42U rack has room for 42U of gear — but its power circuit and cooling envelope usually saturate long before the space does. Real capacity planning weighs all three, per rack, from measured data. That's the difference between a rack diagram and rack management.
Rack Unit Questions
How tall is 1U in inches and millimeters?
1U (one rack unit) is 1.75 inches, or 44.45 millimeters. A 2U server is 3.5 inches (88.9 mm), and a 4U chassis is 7 inches (177.8 mm).
How tall is a 42U rack?
42U of usable space is 73.5 inches (about 1.87 m) of mounting height. With frame, casters, and top panel, a typical 42U cabinet stands roughly 78–80 inches (2 m) tall overall.
How many servers fit in a 42U rack?
Up to 42 1U servers in pure space terms — but power and cooling usually run out first. With switches, PDUs, and cable management taking a few U, and per-rack power budgets, real-world racks often hold 20–35 servers.