What are 1U, 2U, and 3U?
“U” refers to the height of a server chassis.
1U equals 1.75 inches (approximately 4.45 cm), so 3U equals about 3 × 4.45 cm.
“U” (short for unit) is a unit used to indicate the external dimensions of modular racks. The detailed specifications are defined by the U.S. Electronic Industries Alliance (EIA), an industry standards organization.
The specified dimensions are a width of 48.26 cm (19 inches) and a height in multiples of 4.445 cm. Because the width is 19 inches, racks that meet this standard are often referred to as 19-inch racks. The height is measured in basic units of 4.445 cm.
| Specification | Height (mm) | Common Uses |
| 1U | 44.45 mm | High-density servers, network equipment |
| 2U | 88.9 mm | Balanced computing and expansion |
| 3U | 133.35 mm | Local interaction / more user-friendly display |
Common Rack Cabinet Sizes, How Many Servers Can a 42U Rack Hold?
Server dimensions are standardized so that servers can be properly mounted in steel or aluminum racks. Racks have pre-drilled mounting holes that align with the mounting holes on servers, allowing them to be secured with screws. This standardization makes installation easier and ensures that each server occupies the appropriate amount of space.
The standardized dimensions specify a server width of 48.26 cm (19 inches) and a height in multiples of 4.445 cm. Because the width is 19 inches, racks that comply with this standard are often referred to as “19-inch racks.” Height is measured in units of 4.445 cm, where 1U = 4.445 cm. Details are shown in the table below.
- What Are the Dimensions of a 42U Rack?
A 42U rack cabinet typically measures:
- Height: 2.0 meters
- Width: 0.6 meters
- Depth: 0.8 meters
Some models may also have a depth of 0.96 meters, while maintaining the same height and width.
- How Many Servers Can a 42U Rack Hold?
The number of servers that can be installed in a rack is limited. A 42U rack does not mean it can hold 42 units of 1U servers in practice. Space must be reserved for:
- Heat dissipation and airflow
- Equipment installation and maintenance clearance
- Power distribution
- Cable management (top and bottom clearance)
- Additional equipment such as switches, firewalls, and displays
For example, a standard 42U rack can typically hold up to about 20 servers.
Why 20? Even with 1U servers, space must be left between servers for cooling. In addition, the rack usually needs to accommodate at least one switch, which may require around 2U of space.
If 2U servers are used, the rack can generally accommodate around 10 servers, plus additional networking equipment such as switches and routers.
1U / 2U / 3U Chassis and Display Size Design Recommendations
1) 1U Chassis (Highly Space-Constrained)
Feasible Solutions:
- 3″ – 2.4″ OLED / LCD
- Monochrome character displays, dot-matrix modules, or low-resolution color displays
Intended Use Only For:
- Status information
- IP address / temperature / alarms
- Menu navigation
Typical Display Parameters:
- Screen height: ~30 mm
- Resolution: 128 × 64 or 320 × 240
- Aspect ratio: 4:3 or ultra-wide (bar display)
Orient Display offers many monochrome character LCD modules and dot-matrix graphic LCD modules suitable for 1U applications. It also provides a wide selection of small-size color TFT modules. Since most small TFT modules are designed in portrait orientation, they typically need to be rotated 90 degrees for use in 1U systems.
There are also bar displays available on the market that are suitable for 1U applications, such as the 80 × 116 graphic TFT 1U display. In addition, Orient Display offers a 6.9-inch 280 × 1424 capacitive touch display as an option.
2) 2U Chassis (Where It Becomes “Visually Usable”)
This is the starting point for true embedded displays.
Recommended Sizes:
| Screen Size | Usability |
| 3.5″ | Barely interactive |
| 5″ | Recommended |
| 7″ | Upper limit (requires ultra-thin bezels) |
Typical Display Parameters:
- Available height: ~70 mm
- Resolution: 800 × 480 or 1024 × 600
- Aspect ratio: 16:9 or 16:10
Orient Display offers many mid-size color TFT modules suitable for 2U applications, available in both portrait and landscape orientations. For example, 5.0″ 800 × 480 TFT modules are commonly used. In addition, Orient Display also provides 7.8″ 1280 × 400 bar displays with capacitive touch, which are well suited for 2U chassis designs.
3) 3U Chassis (A True “Monitor-Like” Experience)
3U is the most comfortable height for UI designers, offering ample space for layout, typography, and interaction.
Recommended Sizes:
| Screen Size | User Experience |
| 7″ | Safe and reliable |
| 8″ | Best balance |
| 10.1″ | High-end solution |
Typical Display Parameters:
- Available height: ~115 mm
- Resolution: 1280 × 800 or 1920 × 1200
- Aspect ratio: 16:10
Orient Display offers many medium-to-large color TFT modules suitable for 3U applications, available in both portrait and landscape orientations. For example, an 8.0″ IPS TFT (800 × 1280) with all viewing angles, medium brightness, and a MIPI interface is a representative option.
If you have any questions, please contact our engineering.