Server Rack Size Guide 

Server racks and cabinets come in different configurations and sizes - for those new to rack-mounted equipment, understanding the measurements and allowances of server racks will ensure efficient positioning, cable management, and protection for equipment.

If you are not sure about rack unit (RU) measurement, or how to find the right server rack size for your needs, this guide is for you.

Understanding Server Rack Dimensions

Server rack sizing is measured in three dimensions: height, width, and depth. These dimensions dictate the type and configuration of how equipment can be mounted in the server rack. 

*Note: Both imperial and metric measurements are used in server rack sizing to ensure an industry standard that can be used globally.

Server Rack Height

Server rack height is the most common way different rack sizes are classified. Rack enclosure and equipment suppliers use rack units (RU) or units (U) as the standard measure for the distance between shelves in a server cabinet - 1 RU is equal to 1.75 inches or 4.445 cm. 

A full-size server rack is 45 RU, meaning it can support up to 45 individual 1 RU mounts. The 45 RU standard is the most popular size configuration used in data centres, offering ample room for future equipment additions and easy access for maintenance. 

Server rack sizes can be as small as 4RU (usually for wall-mounted cabinets) or as large as 70 RU for open frame racks. Finding the right rack size comes down to the size and number of equipment that requires mounting.

Server Rack Width

The internal width of a server rack is set at 19 inches. This global standard ensures that rack-mounted equipment can be installed correctly regardless of whether it is sourced locally or internationally.

However, some models of server racks have an internal width of 23-inches to support older mounted equipment - 23-inch server racks are not used as widely as 19-inch counterparts, and are more commonly found in telecom applications. 

The external width of server racks can also vary between 600mm and 800mm. Greater external width offers more space to access equipment for cable management and troubleshooting, and does not affect mounting compatibility.

Server Rack Depth

Server rack depth measures the distance between the front and back of the frame. There is no standard sizing for server rack depth - rack depth can range from 300mm to 1200mm to support different equipment dimensions and cabling arrangements. 

The most common server rack depth is 800mm, which provides sufficient space to house mounted equipment and cabling without it extending out of the frame.

Compatibility Considerations for Server Rack Sizes 

Rack height

Given that rack height is always measured in rack units (RU), finding the right server rack size will come down to how much space is needed to house the equipment. 

Adding up the total RU measurement of all required equipment will provide an accurate gauge for the rack size needed. One thing to consider is to add a buffer above the minimum RU height needed - so if you have 22RU worth of equipment to mount, it is best practice to choose a rack enclosure size above it, such as 27RU or 37RU. 

Having additional height for the rack enclosure allows equipment to be spaced out accordingly to avoid overheating issues and increases accessibility when maintenance is required. The extra space also supports opportunities to expand the equipment setup.

Rack width

Rack-mounted equipment is most commonly found in 19-inch width, but can also come in “half-rack” sizes or 23-inch width. 

Finding a server rack to mount 23-inch width equipment is simple enough. The term “half-rack”, however, is usually the source of confusion for those unfamiliar with rack-mounted configurations. 

“Half-rack” can refer to the size of the equipment or the rack enclosure. When used to describe mounted equipment, “half rack” means that the equipment will only take up half of the full 19-inch rack width. For example, a 4 RU half rack unit will take up four rows in height and 9.5 inches in width, allowing two half rack units to be mounted side by side. 

A half rack enclosure refers to an enclosure with a height of 22 RU, half the height of the standard 45 RU enclosure. 

RackLink supplies and manufactures custom rack-mounted solutions for power distribution units (PDUs), MCB distribution boards, and power cables. As a local supplier in Australia, all our products are designed for full compatibility with Australian Electrical Standards. We also offer custom-made power cables and power strips for GPO and IEC connections.