What is a "U" or Rack Unit?

When dealing with servers and similar themed electrical equipment, having proper measurements are integral. It's important to be aware of and take into consideration the server rack depth and height. One beneficial aspect to these measurements is that the Electronic Industries Alliance (frequently abbreviated EIA) created a standard for server racks. This measurement is called a Rack Unit which is boiled down to "RU," but more commonly called a "U." This terminology assists with equipment purchases because industrial and commercial interests often purchase the servers separately from the server rack. In this regard, buyers can purchase the rack system first to erect in advance, then once the servers come in, they can be immediately mounted. Since each server rack sold on Racks2You.com meets EIA standards, standard rack mount servers are guaranteed to fit, regardless of the server brand.

Each Rack Unit is equivilent to 1.75" in height. Therefore, 1.75" H = one U. This unit applies to servers, back-up batteries and other accessories like blanking panels. Since the U measurement is directly correlated to the height of the space, the total Rack Unit measurements are easy to calculate. The internal useable space can be found by multiplying the amount of rack units by 1.75"; so if your rack is 42U and you wanted an estimate internal space just take 42U x 1.75" which comes to 73.5" total internal height available.

Server rack depth is also a consideration. There is no standard for depth; it varies by enclosure and server rack brand. It is important to review a product listing to see if the server rack depth measurement provided is the outside depth or the inside depth. If the measurements provided are inside depth, remember to see what the maximum mounting depth would be. The Geek Racks brand offers an extra deep cabinet rack for server rack accessories that are odd or irregular in shape or size.