Rack Densities Classification in the Age of AI (Jorge A. Gil, Adriana Araujo)

Overview

The article by Jorge A. Gil and Adriana Araujo appears in the Fall 2025 issue (p. 30) of 7x24 Exchange Magazine. It proposes a standard naming scheme for rack density categories. The categories double at each step: LD >0-5 kW, MD >5-10, HD >10-20, VHD >20-40, UHD >40-80, SHD >80-160 and EHD >160-320 kW per rack. A 40 kW/rack boundary is proposed between conventional IT and AI loads, and most current AI systems fall in UHD. Each category is mapped to typical hardware, split into lower and upper levels, and given matching power-per-rack-unit (U) ranges.

The authors recommend defining design density from the actual IT equipment's maximum power per U rather than from industry averages. The industry average is cited as about 6 kW (Uptime 2024) or about 12 kW per rack depending on the survey, and averages should not be used as design density. The method: take the reference server's maximum power, divide by its rack units and multiply by the U allocated to that equipment type.

Each category has a lower level whose upper limit is 75% of the category's upper limit (50% for LD), and power-per-U ranges assume 40 active U. The lower bound for power-per-unit utilization is set at 85% to limit efficiency loss in operation. Limit: this is an authors' naming proposal, not an official standard.

Key points

1. Categories: LD >0-5 kW, MD >5-10, HD >10-20, VHD >20-40, UHD >40-80, SHD >80-160, EHD >160-320 kW per rack.
2. 40 kW/rack is proposed as the boundary between conventional IT and AI loads; most current AI systems fall in UHD.
3. Industry average density is cited as about 6 kW (Uptime 2024) or about 12 kW per rack; averages should not be used as design density.
4. Design density method: reference server max power divided by its rack units, times the U allocated to that equipment type.
5. Each category's lower level tops out at 75% of the category's upper limit (50% for LD); power-per-U ranges assume 40 active U.
6. The lower bound for power-per-unit utilization is 85% to limit efficiency loss in operation.

Using it in design

• Adopt these category codes (LD...EHD) as a rack density class derived automatically from kW/rack.
• Drive default cooling suggestions from the class (for example UHD and above leads to liquid cooling).
• Offer a design-density calculator from server kW per U times allocated U.
• Avoid using industry averages as design density.

Who should read it

Power and cooling designers and capacity planners working on high-density and AI racks.

Publication details

Authors

Jorge A. Gil; Adriana Araujo

Publisher

7x24 Exchange Magazine

Year

2025

Document number

Fall 2025 issue, p. 30

Document language

English

Source type

Industry body

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation