Tool
Rack U-space planner
A rack elevation plans device positions in a cabinet before a rack-and-stack job. Each device occupies a range of U from its start position, and the plan flags overlaps, out-of-bounds devices and the largest free block for what is left to install.
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Your rack
Rack
Usable height: 1866.9 mm
Devices
Rack elevation
40U free
Largest free block: 40U. Total power: 450 W. Total weight: 0 kg.
front view
rear view
How this is worked out
Every assumption is on this page and every input is yours to change. A planner with hidden rules is a persuasion device rather than a tool.
One rack unit is 44.45 mm (1.75 in). A 42U rack gives 1866.9 mm of usable height. Devices occupy contiguous units from their start position, and a full-depth device blocks both front and rear at those units.
The auto-place button fills the lowest free contiguous slot from the bottom, which is where heavy devices belong for stability.
Questions about rack planning
How is rack space measured?
Rack space is measured in U, where 1U is 44.45 mm (1.75 in). A 42U rack gives 1866.9 mm of usable height. Devices occupy contiguous units from their start position.
What is front and rear?
Front and rear refer to the two faces of a rack. Most devices mount at the front. Some devices like cable management mount at the rear. Full-depth devices occupy both faces at once.
How does auto-place work?
Auto-place fills the lowest free contiguous slot from the bottom. Heavy devices belong at the bottom for stability, so the algorithm starts there and works upward.
What is the largest free block?
The largest free block is the biggest contiguous run of empty U. This matters more than total free U, because a 4U device needs 4 contiguous units, not 4 scattered singles.
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