The “Rack Unit” is a standard measurement for server height; one rack unit (U) is 1.75 inches.

When leasing space in a colocation facility (or planning for an on-site network cabinet or closet), customers should focus on four key issues:

1. space: cabinet or rack width is almost always 19 inches; depth may range from “less than 30” to “more than 40” inches, and height is measured in “rack units” (below);
2. bandwidth: 10Mbps, 100Mbps, 1Gbps, 10Gbps; this might be “flat rate” or might impose surcharges when usage exceeds certain levels; also be sure to understand whether your bandwidth is shared with other users on the same switch port;
3. power: if you lease fractional space in a cabinet, you might be allocated one to five amps (1A to 5A) of power; for a full cabinet, you might be allocated a maximum of 15A to 20A (note that average power usage should not exceed 80% of the total, so 15A max = 12A average).
4. heat:  You must also pay attention to airflow and cooling; if you lease a full cabinet and fill it completely with equipment, you’ll probably need far more than 15A power, and the heat generated by the equipment might exceed the cooling capacity, causing some equipment (especially at the top) to malfunction.

Here is a “Rack Unit Calculator” grid:

One Response to “Rack Unit Calculator (leasing rack space in cabinets)”

1. dan says:

   November 28, 2017 at 4:57 pm

   Nice article! I’ve seen up to 11′ racks 83U for some of our clients.