It's clear that a good server rack involves much more than just IT storage. However, while there are many variables to consider (pre-configured versus custom racks, open versus closed racks, or 2-post versus 4-post racks, to name just a few), choosing the right server racks starts with understanding your IT storage space and the dimensions of the server racks. This includes three sets of measurements: server rack height, server rack width, and server rack depth.

The industry has largely standardized these three measurements to help ensure components fit any rack brand you choose. But even though common sizes are widely available, you still need to understand the three main dimensions of server racks and what they mean to properly plan your data center.
Here's what you need to know about server rack sizes.

Server Rack Height
When discussing standard server rack sizes, the term 42U rack is often part of the conversation. This dimension specifically refers to the rack's height. U, or sometimes RU, stands for unit or rack unit. One rack unit, or U, is equal to 1.75 inches or 44.45 millimeters. Therefore, a 42U rack provides a total of 73.5 inches of available vertical space for equipment.
Other common and widely available server rack heights include 22U and 27U (generally referred to as half racks) and extra-large 48U cabinets intended for high-density data center operations. Compact wall-mount racks as small as 1U are also available, which may be all that is needed for a small office application.
U not only applies to the height of the server rack; it is also used to designate the height of the IT devices that will be mounted within the racks. Most devices (servers, PDUs, UPS units, KVM switches, and patch panels, for example) are classified into 3U, 2U, or 1U sizes. Determining how many devices can fit in the rack is simply a matter of adding up the dimensions of each device and ensuring they don't exceed the rack's height. Of course, you'll always want to leave some room for future growth and additional equipment.

Server Rack Width
Another standard server rack dimension you'll frequently hear about is the 19-inch rack. This measurement refers to the rack's width. However, it's important to clarify that this specifically refers to the mounting width, not the entire external width of the server rack. Many server rack exteriors are 24 inches wide or even wider, which is important to know when setting up your server room and determining how many racks will fit in your available 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 screwing or clipping the front panel to the rack. Generally, a 19-inch server rack allows for dense hardware configurations without taking up much space or shelf space.

Server Rack Depth
The remaining piece of the three rack server dimensions is the server rack depth, or the distance between the front and rear rails of the rack. Depths can range from 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 - Medium deep
• 42 inches - Deep

Keep in mind that these numbers are actual depths. The usable depth is always slightly less. A small amount of clearance must be left at the front and rear of the rack to allow for door openings and rail mounting. Typically, this clearance is about 0.875 inches at each end of the rack, for a total of 1.75 inches. Some additional space will also be needed for cable connections, accessories, and airflow.
Therefore, you'll need a usable rack depth that's slightly deeper than that of your largest piece of equipment. The good news is that newer server rack cabinets often include adjustable mounting rails. You can choose a deeper rack to give yourself some flexibility and then position the rails at the ideal depth for each server or piece of equipment housed in the rack.

Stick with the standard? Or opt for a custom solution?
The most common server rack size is 42U high and 19 inches wide. These standard server racks tend to be cost-effective because they are mass-produced for use in data centers. However, some businesses or applications require different or unique server rack sizes. If standard sizes don't meet your needs, rest assured that you can customize a solution in all three dimensions of the server rack to perfectly fit your application's unique requirements.
Once you have the right server rack size, you'll be on your way to choosing the best server racks for your data center. Now you can move on to more strategic considerations about server racks, including doors, grounding, accessories, security, and IT rack cooling. To learn more about these important considerations, read our article: How to Select an IT Rack?

Vertiv Server Racks Available:
Vertiv offers a complete portfolio of racks, cabinets, and enclosure solutions for data centers, including a full range of rack accessories, to support and protect your critical IT equipment. Every Vertiv server rack is designed for optimal performance with ease of 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 variety of equipment, including servers, storage, switches, routers, PDUs, UPS units, console port servers, and KVM switches. The flexible rack offers a full range of accessories, including cable management, airflow management, support trays and brackets, doors and security, and service parts. Tool-less options allow for quick installation and setup.

Knurr Mir2 Server Rack: The Knürr® DCM server rack is a modular, aluminum-framed rack designed to protect high-density server and network applications in IT environments with its 1500 kg load capacity. It guarantees unparalleled levels of efficiency, security, and scalability thanks to its robust design, optimal precision cooling capabilities, and flexible configuration and customization features.

Knurr DCM Server Rack: The Vertiv Knurr MIR2 server rack is a highly versatile, state-of-the-art infrastructure solution designed to house and protect server equipment in a variety of IT environments. It features adjustable mounting rails and a robust frame structure capable of supporting substantial equipment weight. Its innovative airflow management, combined with perforated doors, ensures optimal cooling efficiency. A classic among innovative racks, the Vertiv Knurr MIR2 server rack boasts a wide range of optional accessories and upgrades to meet diverse customer requirements.