Guide
Planning rack space, power, heat and weight before installation
A rack is a small budget with four lines: space, power, cooling and weight. Running out of any one of them stops a deployment, and they are easy to overlook until the equipment has arrived. The planner takes the list of devices you intend to install and totals all four, with a diagram of which unit each occupies.
What you enter
Set the rack height in units, then add equipment: a name, height in U, power draw in watts, weight in kilograms and a quantity. Quantity expands into numbered copies in the layout, such as “Server (3 of 6)”. The Sample button loads a complete small plan. Equipment is stacked from the bottom in the order of the list, so list heavy items first, and a final line reports the free space above.
The conversions
A rack unit is 44.45 mm (1.75 in), and a standard full-height rack is 42U, though 45U, 48U and half-height cabinets exist. Power ends up as heat, so the heat load in BTU per hour is the watts times 3.412. Current follows from power divided by voltage, so the page shows the amps at both 230 V and 120 V. Electrical codes and good practice keep a circuit below about 80 percent of its rating for continuous loads, so a 16 A circuit should carry no more than about 12.8 A. Use the nameplate or measured power rather than the maximum PSU rating when you have it, since most devices run well below the maximum.
What it does not know
The planner counts height, power and weight but not depth, mounting rails, cable management, airflow direction or blanking panels. Equipment that is deeper than the rack, hot-aisle and cold-aisle layout, power distribution units, and the floor’s load capacity are outside the calculation. Also check the rack’s rated weight capacity and the cooling available at the location, since a rack can fit physically and still overheat the room.
A worked example
The sample plan has two patch panels, two 48-port switches, two firewalls, six servers of 2U, a 4U storage array and a 3U UPS. That is 25 of 42 units (60 %), leaving 17 free. The total draw is 4,130 W, which is 14,092 BTU/h (4,130 × 3.412), or 18.0 A at 230 V and 34.4 A at 120 V. The weight is 263 kg. In the layout the patch panels occupy U1 and U2, the switches U3 and U4, the firewalls U5 and U6, the servers U7 to U18, the storage array U19 to U22 and the UPS U23 to U25. U26 to U42 are free.
Limits
The figures are as good as the numbers you enter. Manufacturers list a maximum draw and a typical draw, and the difference can be large, so choose one deliberately. The page does not store the plan on a server; it stays in your browser. Network cabling for the rack, including the length limits, is in the Network Cable Chart, and the storage you are installing can be sized with the RAID Calculator.
Related tools
- RAID Calculator sizes the arrays in the storage chassis.
- PoE Power Calculator adds the PoE load switches must supply.
- Network Cable Chart shows what the patch panels may carry.
- SLA Uptime Calculator converts redundancy plans into expected downtime.
Checked against the current version of the Server Rack Planner on .