What is “U” in a Server Rack? Understanding Rack Unit Measurement

The selection of a proper server rack size is one of the most complicated and, meanwhile, important parts of IT system setup. The importance of correct rack size selection is explained by possible hazards that can happen if the model is chosen incorrectly. These include equipment damage, malfunction, overheating, and increased deterioration. This is why it is essential to determine the best rack size.

The height comes as the trickiest parameter. Firstly, you should know that the height is measured in U. So, we should start by answering what does the U mean in server racks. U is the abbreviation for Unit. 1U is equal to 1,75 inches. Thus, when you see such designations as “12U”, “24U”, or “4U” in the name of rack models, they denote the height.

How did Rack Unit become a Standard?

The unit was set by the EIA (Electronic Industries Association) to simplify buying matching parts for rack setup. The introduction of this unit standardized relations in the industry and simplified the lives of system administrators. It became easier to calculate and find matching rails and posts with the needed holes.

Modern manufacturers produce a wide range of model sizes, starting from 1U and going up to 48U. According to the number of Us, furniture falls into 3 major groups:

  1. Full-size racks. These are the biggest floor-standing models of 42U-48U sizes. They are incredibly spacious and capacious. They can accommodate dozens of servers, hundreds of active devices, and accessories.
  2. Half models. These products are typically sized from 14U to 20U. Yet, the most common sizes of this class are 22U and 27U server rack. Both floor-standing and wall-mount models are found.
  3. Quarter racks. These products are the smallest. The maximum size reaches 14U, with 11U being the most popular one. In most cases, such models are designed for desktop installation or fastening to walls.

The most popular rack models are 6U, 9U, 12U, 18U, 22U, 37U, 42U. Here’s a grid with the most popular rack heights and their dimensions in different systems:

Rack UnitsInchesFeetCentimeters

How to evaluate the needed amount of Us?

Now, when we clarified what 1 U rack size is, we can proceed to the guide on how to select a suitable height of the server cabinet. The first thing to note is that a standard server is 1U tall. Thus, by calculating the number of servers in your network system, you can set a minimum size. Further, add the heights of other active devices and space-consuming components. At this stage, pay attention to:

  • other devices and passive hardware that are 1-75-inch high;
  • how much Us you need to leave to house smaller devices and accessories;
  • if some devices take up more space than 1U, account 2Us for them.

It is very helpful to make 3D visualization with a digital layout. In this case, you’ll be able to find out and eliminate all mistakes at the planning stage. This approach allows for designing the most ergonomic layout. When designing the setup to determine the required furniture size, consider colocation. Make sure to place devices loosely and leave enough room for cable routing and fans.

Here are some basic principles for designing the best layout:

  1. Leave space along the sides of racks for wiring cords are installing cable management tools.
  2. Define places for ventilation fans, if needed.
  3. Place heavy equipment on the bottom and light devices on top.
  4. Consider the airflow direction to achieve the best cooling.

Finally, calculate the height and add a quarter or even a half of the size. For what purpose? Digital development is an ongoing process. Most businesses encounter the need to increase computing power by adding extra devices and reinforcing IT systems. Thus, it is likely that you’ll need to install new hardware pieces in the future. Leaving free space at once will help avoid the need to buy another furniture piece.

Additional Consideration for Determining the Required Rack Size

Knowing server rack U meaning is not enough to select the best model. Other important parameters include:

  1. Security. Think about the circle of authorized employees who will have access to your server rack. Also, here, it is important to define where it will be placed (public or closed premises). Access to vulnerable IT equipment must be strictly limited to avoid damage and datum loss.
  2. Power draw. Make sure that an available PDU is disposable to feed your IT system. The bigger the rack is, the more devices it can accommodate, thus, the most power it needs to feed all units.
  3. Maintenance. The smoothness and durability of IT systems highly depend on their timely and effective maintenance and hazard elimination. The staff should have easy and comfortable reach to devices so that ensure an uninterruptible functioning of all units.

IT systems are the heart and brain of any modern facility. Thus, a data center stands behind each business. The proper furnishing of data centers directly influences hardware performance. Server racks are designed to store equipment pieces reliably, accommodate all sorts of components, and secure them from negative external impacts. Yet, the selection of an appropriate size is a responsible task that requires attention.

When you know the answer what U in rack size is, it is easier for you to select the needed model. However, make sure to keep in mind all the criteria mentioned above. Otherwise, if you fail to pick the right size, it can result in malfunction, break, and overheating.

If you have any questions, please ask below!