TradesHow this works
A rack is measured in rack units, and one unit is 1.75 inches on a standard 19 inch rack. Every device is built to a whole number of units, so sizing a rack is really just adding those up. The catch is that the number you want is not the sum, it is the sum plus room to breathe.
This adds up your gear, then sizes to the growth headroom you set so the rack keeps space for airflow gaps, cable management, and the next device. It calls wall-mount versus floor-standing, offers the next size up when you want more room, and estimates the heat the gear puts into the room so you can plan cooling.
Common questions
How many rack units do I need?
Add up the height of every device at its standard size: switches, routers, firewalls, and patch panels are 1U each, a 2U server is 2U, and a rackmount UPS is about 2U. That sum is your gear height. Then you want a rack taller than that, because a rack filled to the top has no room for airflow, cable management, or the next thing you add.
How much empty space should a rack have?
A common target is to keep roughly a quarter of the rack free for growth and airflow. Packing every unit leaves no room for cable managers, blanking panels, or the next switch, and it makes the rack run hotter and harder to service. This tool sizes to the headroom you set, so you land on a rack that fits today and tomorrow.
Wall-mount or floor-standing?
Wall-mount cabinets are convenient and save floor space but top out around 15U and are shallow, so deep servers may not fit. Once the build passes that, or you are racking servers and a UPS, a floor-standing cabinet gives you the depth and takes the weight. The tool calls which one your size lands on.
Sources: Rack-unit geometry: EIA-310 19 in rack, 1U = 1.75 in (evergreen) · Equipment RU heights: standard nominal gear sizes. Engine version 1.0.0. Risk tier 1.