What Size Server Rack Do I Need? Rack Calculator and Standard Sizes
Feb 17th 2026
Choosing the correct server rack height is one of the most important steps in building or upgrading an IT environment. An undersized rack limits airflow and future expansion, while an oversized rack can waste valuable floor space.
To make this easier, we’ve included an interactive server rack size calculator below, along with real-world examples and a complete buying guide.
What Is a Rack Unit (U)?
Server rack height is measured in rack units (U).
One rack unit equals 1.75 inches (44.45 mm), as defined by the EIA-310 used across the IT industry.
Common Server Rack Heights
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6U – 12U: Small networks, wall-mount racks
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18U – 27U: Network closets, edge deployments
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32U – 42U: Server rooms, data centers
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45U – 48U: High-density enterprise environments
How to Calculate Server Rack Height
To calculate manually:
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Add up the U space required for each device
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Include space for:
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Cable management
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Airflow gaps
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Power distribution
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Add 20–30% extra capacity for future growth
Server Rack RMU Calculator
Estimate how tall of a server rack you need based on your equipment.
| Equipment | Quantity | U per Device |
|---|---|---|
| Rackmount Servers | ||
| Network Switches | ||
| Patch Panels | ||
| UPS Systems | ||
| Other Rack Equipment |
Total Rack Units Needed:
Recommended Rack Size:
What Is a Rack Unit (U)?
Common Rack Heights
Server rack height is measured in rack units (U).
One rack unit equals 1.75 inches (44.45 mm), defined by the EIA-310.
- 12U – Small networks & wall-mount racks
- 24U – Growing SMB environments
- 42U – Standard data center rack
- 48U – High-density deployments
Server Rack Width
Typical Rack Depths
Depth
Best For
24–30”
Network equipment, wall-mount racks
32–36”
Short-depth servers
42–48”
Full-depth enterprise servers
Best practice:
Measure your deepest server and add 3–6 inches for cabling and airflow.
Server Rack Dimensions by Manufacturer
While rack height is standardized in rack units (U), external dimensions vary by manufacturer. Use the dropdowns below to compare typical external height, width, and depth for common rack sizes.
View APC Rack Dimensions
| Rack Size | Height | Width | Depth |
|---|---|---|---|
| 42U | 78–79 in | 23–24 in | 42–48 in |
| 24U | 45–50 in | 23–24 in | 36–42 in |
View CPI Rack Dimensions
| Rack Size | Height | Width | Depth |
|---|---|---|---|
| 42U | 78–80 in | 23–24 in | 36–48 in |
| 48U | 84–87 in | 23–24 in | 42–48 in |
View Tripp Lite Rack Dimensions
| Rack Size | Height | Width | Depth |
|---|---|---|---|
| 42U | 73–75 in | 23–24 in | 39–42 in |
| 25U | 52–55 in | 23–24 in | 36–42 in |
View Great Lakes Rack Dimensions
| Rack Size | Height | Width | Depth |
|---|---|---|---|
| 42U | 78–79 in | 23–24 in | 36–48 in |
| 24U | 47–50 in | 23–24 in | 36–42 in |
View Kendall Howard Rack Dimensions
| Rack Size | Height | Width | Depth |
|---|---|---|---|
| 42U | 80.50 in. | 23.5 & 31.5 in | 37.75–38.00 in |
| 24U (2-post) | 47.375 in | 20.8125 in in | 15.04 in |
Planning Tip:
Always verify:
External height (for ceiling clearance)
External depth (for doors, aisles, and cabling)
Weight ratings for loaded equipment