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How Many 1U Servers will Fit in a Rack?

Just like warehouses store products, data centers are warehouses for digital information. They contain things like servers that are used to host websites. Businesses often outsource their web hosting, data storage, and information technology needs to data centers because it’s cheaper, data centers are more reliable than most in-house operations, and they’re often more secure than businesses’ in-house operations.

One of the most prevalent components of data centers is servers used to host websites. These servers are frequently stacked on top of one another to save room on large server racks that are dedicated to the exclusive storage of servers.

To answer the question of how many 1U servers will fit in a server rack, we first need to define what 1U means.

What is a standard rack unit?

Just like temperature and pressure are measured with degrees of Celcius or Fahrenheit and pascals, respectively, standard rack units are used to indicate how large servers are.

In the field of data center colocation, the sizes of servers are expressed in standard rack units, which are often abbreviated as U or RU, respectively.

Virtually all modern servers are the same width and length. The only thing different about their size is how tall they are. One unit or rack unit equates to a height of 1.75 inches, or 44.45 millimeters.

A server that is 1.75 inches tall is given a rack unit size of 1U. One that is seven inches tall, for example, is given a rack unit size of 4U.

How big are server racks?

Just how servers come in different sizes, racks come in different sizes, as well. Racks, which are almost always constructed entirely out of metal, are sturdy frames that hold individual servers.

The three main sizes of server racks of full racks, half racks, and quarter racks.

Full racks hold 42 rack units’ worth of servers stacked on top of one another. In other words, full racks hold about six feet of servers in terms of height.

Half racks hold anywhere between 18 rack units and 22 rack units, or roughly three feet of servers stacked on top of one another.

Quarter racks generally hold between 10 and 12 rack units’ worth of servers, which comes out to about 1.5 feet of servers.

Server racks also feature side-by-side columns to hold servers with. When shopping for racks, data center managers can simply refer to racks’ specifications to figure out whether they have multiple columns or just one.

Why are there different sizes of racks to hold servers?

Some facilities have very high ceilings. In such facilities, data centers are able to store dozens, if not hundreds, of servers stacked on top of one another. Other facilities have standard eight-foot or 10-foot ceilings, in which managers usually don’t house anything taller than single full racks.

Data centers need to know what size various racks are in order to plan out their server-hosting infrastructure. The aforementioned units of measurement exist to make such planning easier.