A server rack houses and organizes critical rack-mounted IT devices and equipment found in a data center or computer closet. Server racks are the backbone of a good physical infrastructure design that lets your business take full advantage of your IT systems and capacity. The right rack helps to optimize floor space and energy efficiency while ensuring the physical protection and security of the sensitive IT systems inside.
Clearly, there is much more to a good server rack than just IT storage. However, while there are many variables to consider (preconfigured versus customized, open racks versus enclosed racks, and 2-post racks versus 4-post racks, to name just a few), getting your server racks right starts with understanding the IT storage space, or the server rack dimensions. This includes three sets of measurements: server rack height, server rack width, and server rack depth.
In large part, the industry has standardized these three measurements to help ensure that components will fit into any brand of rack you choose. But even though common sizes are widely available, you still need to understand what the three main server rack dimensions are and what they mean, so you can properly plan your data center.
Here is a closer look at what you need to know about server rack sizes.
Server Rack Height
When talking about standard server rack sizes, the term 42u rack is usually part of the conversation. This dimension specifically refers to the height of the rack. U, or sometimes RU, is the abbreviation for unit or rack unit. One rack unit or U is equivalent to 1.75 inches or 44.45 millimeters. So, a 42U rack provides a total of 73.5 inches of available vertical equipment space.
Other common and widely available server rack heights include 22U and 27U (usually referred to as half racks) and extra-large 48U enclosures intended for high-density data center operations. Compact wall-mount racks are also available as small as 1U size, which may be all that is needed for a small office application.
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U not only applies to server rack height; it is also used to designate the height of the IT devices that will be mounted inside the racks. Most devices (servers, power distribution units, uninterruptible power supply units, KVM switches, and patch panels, for example) are classified as a 3U, 2U, or 1U size. Determining how many devices can fit inside the rack is simply a matter of adding up the sizes of each device and ensuring they do not exceed the height dimensions of your rack. Of course, you always want to leave some room to spare for growth and additional equipment you may need to add in the future.
Server Rack Width
Another standard server rack dimension you will hear used frequently is 19-inch rack. This measurement refers to rack width. But it is important to be clear that it refers to the mounting width specifically, and not to the full exterior width of the server rack. Many server rack exteriors are 24 inches wide or even wider, which is important to know when configuring your server room and determining how many racks will fit into the available floor space.
On a device like a server, the mounting width is measured from one mounting hole or bracket to another. The device is then mounted by bolting or clipping the front panel to the rack. Generally, a 19-inch server rack permits dense hardware configurations without taking up a lot of floor space or shelving.
Server Rack Depth
The remaining piece of the rack server dimensions trifecta is server rack depth, or the distance between the front rail to the back rail of the rack. Depths can range from just a few inches to 50 inches or more. However, the most common standard depth dimensions for server racks are as follows:
- 27 inches - Shallow
- 31 inches - Moderately deep
- 37 inches - Average depth
- 42 inches - Deep
Keep in mind that these numbers are actual depths. Usable depth is always a little bit less. A small amount of space must be left in the front and the back of the rack to allow for doors to open and for the rails to be mounted. Typically, this depth is approximately 0.875 inches at each end of the rack, for a total of 1.75 inches. Some additional space will also be needed for wire connections, accessories, and air flow.
So, you will need a usable rack depth that is a bit deeper than your largest piece of equipment. The good news is that newer server rack enclosures often include adjustable mounting rails. You can choose a deeper rack to give yourself some wiggle room, and then place the rails at the ideal depth for each server or piece of equipment housed in the rack.
Stick with the standard? Or go with a custom solution?
The most common server rack size is 42U height and 19-inch width. These common server racks tend to be cost-effective because they are mass-produced for use in data centers. However, some companies or applications do require different or unique server rack sizes. If the standard sizes don’t meet your needs, rest assured that you can customize a solution across all three server rack dimensions to perfectly fit the requirements of your unique application.
Once you have the server rack size right, you are on your way to choosing the best server racks for your data center. Now, you can move on to more strategic server rack considerations, including doors, grounding, accessories, IT rack security, and IT rack cooling. For more on these important considerations, read our article: How Do You Select an IT Rack?
Server racks available from Vertiv
Vertiv offers a comprehensive portfolio of data center racks, cabinets, and enclosure solutions, including a full spectrum of rack accessories, to support and protect your critical IT equipment. Every Vertiv server rack is designed for optimal performance with easy deployment and scalability in mind. Our most popular server racks, available in all standard server rack sizes, include:
Vertiv™ VR Rack: The Vertiv VR rack supports a wide variety of equipment including servers, storage, switches, routers, PDUs, UPS units, console port servers, and KVM switches. The flexible rack offers a comprehensive lineup of accessories including cable management, air flow management, shelves and support brackets, doors and security, and service parts. Tool-less options allow for quick installation and configuration.
Vertiv™ DCE Optimized Rack Systems: The Vertiv DCE rack system provides a flexible foundation for infrastructure support. It is available pre-configured or can be fully customized with your choice of factory-installed accessories to create the perfect server rack for your needs and data center environment.
Go online today for details on all Vertiv™ rack and enclosure options.