Skip to content
ENExplore Calculators

Rack Unit Space Calculator

Work out rack unit space instantly with clear inputs, formula shown and shareable results.

About Rack Unit Space Calculator

Rack planning must reserve space as well as count equipment: a standard 42U rack should be filled to about 85 percent so there is room for cable management, blanking panels and future additions, and so airflow is not obstructed. Power and cooling density usually limit a rack before its physical height does.

Formula

Rack space

used = servers x U per server + infrastructure U; racks = ceil(used / (rack height x 0.85))

Worked example

With the default values below, Rack Unit Space Calculator returns Rack units consumed of 48.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Serversminimum 0
18
Rack units per serveraccepts 0.5–10 U
2 U
Network, PDU and management unitsminimum 0 U
12 U
Rack heightaccepts 1–60 U
42 U

Results

Rack units consumed
48.0 U
Racks required
2
Free units per rack
18.0 U
Rack space utilisation
57.1%

Step by step

  1. 1Values used
  2. 2Rack space
  3. 3Rack units consumed= 48.0 U
  4. 4Racks required= 2
  5. 5Free units per rack= 18.0 U
  6. 6Rack space utilisation= 57.1

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why not fill a rack completely?

Cable managers, blanking panels and access all need space, and a full rack is difficult to work in. Power and cooling limits also usually bind first.

What limits rack density in practice?

Available kilowatts per rack and the cooling to remove that heat. Many facilities cap at 5 to 10 kW per rack, which fills long before 42U does.

Related Calculators

Rack Unit Space Calculator – Calculate Rack units consumed