What is PUE (power usage effectiveness)?

The PUE formula

PUE = total facility energy ÷ IT equipment energy.

IT equipment energy is what the computing hardware itself uses: compute, storage and network equipment[6]. Total facility energy is that plus everything that keeps the hardware running, from power delivery components to cooling and lighting[6]. The National Renewable Energy Laboratory states the same ratio in terms of power: total power used by the facility over the power delivered to its computing equipment[7].

A worked example: a data center whose servers, storage and network gear draw 100 megawatts, and which spends another 50 megawatts on cooling, power conversion and lighting, uses 150 megawatts in all. Its PUE is 150 ÷ 100 = 1.5. Put another way, for every unit of power that reaches the computers, half a unit more goes to overhead.

What is a good PUE?

Lower is better, and 1.0 is the floor the formula allows. The Department of Energy puts the average data center at 1.6 and says several recent super-efficient sites have gone below 1.1[8]. Uptime Institute’s 2026 survey of operators puts the industry average at 1.52[1], barely changed from the 1.54 weighted average in its 2025 survey[2]. Google reports a fleetwide average of 1.09 for 2025[3], and Facebook said in 2011 that its first dedicated data center, in Prineville, Oregon, reached an initial PUE of 1.07[9]. Those last two are company-reported.

How PUE has changed

Uptime Institute says the industry average dropped fast between 2007 and 2014, from 2.5 to 1.65, as operators picked off the cheapest, most practical improvements first[2], and had barely moved for six years by 2025[2]; the 2026 survey put it at 1.52[1]. Lawrence Berkeley National Laboratory credits the same kinds of gains, better cooling and power management among them, for holding U.S. data center energy use flat from 2014 to 2016[5].

Where the overhead goes

Mostly into cooling. The Department of Energy says cooling can account for as much as 40% of a data center’s energy[10], and a 2025 Congressional Research Service report put it at 38% to 40%[11]. That is why cooling design drives PUE, and why liquid cooling matters for AI: liquid can carry about 1,000 times as much heat as air[12]. How are data centers cooled? covers the options.

What PUE doesn’t tell you

PUE measures overhead, not impact. It says nothing about water: The Green Grid built a separate metric, water usage effectiveness (WUE), in liters per kilowatt-hour, to be read alongside PUE and a carbon metric[13]. The two can pull against each other. CRS says evaporative cooling is generally more energy efficient than air-cooled chillers, which use no water but more energy[14], and Microsoft says its zero-water cooling design will raise its PUE, with what it calls a nominal increase in annual energy use[15].

PUE is also a ratio, not a total. A very large campus with an excellent PUE can still use far more electricity than a small, inefficient one; how much electricity data centers use has the totals.

Common questions

What is PUE?

Power usage effectiveness: a data center’s total electricity use divided by the electricity used by its IT equipment. A PUE of 1.5 means that for every unit of power reaching the computers, another half unit goes to cooling, power conversion and other overhead.

What is a good PUE for a data center?

Lower is better, and 1.0 is the theoretical minimum. The Department of Energy puts the average data center at 1.6 and says some recent super-efficient sites have gone below 1.1; Uptime Institute’s 2026 survey put the industry average at 1.52.

How do you calculate PUE?

Divide the total energy the facility uses by the energy its IT equipment uses. A data center using 150 megawatts in all, of which 100 reach the servers, storage and network equipment, has a PUE of 1.5.

What is Google’s PUE?

Google says its global data center fleet averaged a PUE of 1.09 in 2025.

Does a low PUE mean a data center is green?

Not on its own. PUE measures energy overhead, not water use or carbon. The Green Grid’s water usage effectiveness metric is meant to be read alongside it, and cooling that saves energy often uses more water.

Sources

1. Uptime Institute Global Data Center Survey 2026
   Uptime Institute (Uptime Intelligence), UII Keynote Report 209 · 2026-07
   Source excerpt

   “The 2026 industry average PUE is 1.52”

2. Uptime Institute Global Data Center Survey 2025
   Uptime Institute · 2025-07
   2 source excerpts

   “The industry's average dropped quickly — from 2.5 in 2007 to 1.65 in 2014 — as operators first deployed the most practical and economical changes.”

   “In 2025, respondents' annual PUE had a weighted average of 1.54 (see Figure 2), marking the sixth consecutive year that this headline figure has virtually stood still.”

3. Power usage effectiveness – Google Data Centers
   Google · 2026
   Source excerpt

   “In 2025, the average annual power usage effectiveness for our global fleet of data centers was 1.09.”

4. Data Centers and Their Energy Consumption: Frequently Asked Questions (R48646)
   Congressional Research Service (via EveryCRSReport.com) · 2026-05-12
   Source excerpt

   “An expression or metric sometimes used to describe the energy performance of data centers is power usage effectiveness (PUE), which is the ratio of all the power used by the data center to the power used by just the IT equipment.”

5. 2024 United States Data Center Energy Usage Report
   Lawrence Berkeley National Laboratory · 2024-12-20
   3 source excerpts

   “Power Usage Effectiveness (PUE) is defined as the total electricity demand of the data center divided by the electricity demand of the IT equipment.”

   “U.S. data center annual energy use remained stable between 2014–2016 at about 60 TWh”

   “The efficiency strategies that allowed the industry to avoid increased energy needs during this period included improved cooling and power management, increased server utilization rates, increased computational efficiencies, and reduced server idle power.”

6. Data Center Metering and Resource Guide
   U.S. Department of Energy Better Buildings (hosted by Lawrence Berkeley National Laboratory) · 2017-02
   2 source excerpts

   “Total facility energy includes all IT equipment energy as described above, plus everything that supports the IT equipment using energy, such as: Power delivery components...Cooling system components...Lighting.”

   “IT equipment energy includes the energy associated with all of the IT equipment (e.g., compute, storage, and network equipment).”

7. High-Performance Computing Data Center Power Usage Effectiveness
   National Renewable Energy Laboratory · 2026
   Source excerpt

   “PUE is the ratio of the total amount of power used by a computer data center facility to the power delivered to computing equipment.”

8. Best Practices Guide for Energy-Efficient Data Center Design (Revised July 2024)
   U.S. Department of Energy, Federal Energy Management Program · 2024-07
   Source excerpt

   “An average data center has a PUE of 1.6; however, several recent super-efficient data centers have been known to achieve a PUE below 1.1.”

9. Facebook Launches Open Compute Project
   Meta (Facebook Newsroom) · 2011-04-07
   Source excerpt

   “This technology enabled the data center to achieve an initial power usage effectiveness (PUE) ratio of 1.07, compared with 1.5 for our existing facilities”

10. DOE Announces $40 Million for More Efficient Cooling for Data Centers
    U.S. Department of Energy · 2023-05-09
    Source excerpt

    “data center cooling can account for up to 40% of data center energy usage overall”

11. Data Centers and Their Energy Consumption: Frequently Asked Questions (R48646)
    Congressional Research Service · 2025-08-26
    Source excerpt

    “The cooling systems could account for another 38% to 40% of electricity consumption in a data center.”

12. High-Performance Computing Data Center Warm-Water Liquid Cooling
    National Laboratory of the Rockies (formerly National Renewable Energy Laboratory) · 2025-12-04
    Source excerpt

    “Liquid has approximately 1,000 times the cooling capacity of air. … And rack power densities of 60 kilowatts (kW) per rack or more can be achieved using warm-water liquid cooling, which requires less floor space.”

13. Water Usage Effectiveness (WUE): A Green Grid Data Center Sustainability Metric (White Paper #35)
    The Green Grid · 2011
    Source excerpt

    “The new water usage effectiveness (WUE™) metric—combined with the PUE and carbon usage effectiveness (CUE™) metrics—enables data center operators to quickly assess the water, energy, and carbon sustainability aspects of their data centers. ... The units of WUE are liters/kilowatt-hour (L/kWh).”

14. Data Centers and Water: Frequently Asked Questions (R49057)
    Congressional Research Service (via EveryCRSReport.com) · 2026-07-31
    Source excerpt

    “Trade-offs in water consumed and power usage exist between evaporation-based cooling systems and air-cooled systems. Evaporation-based cooling systems are generally more energy efficient than air-cooled chillers or other waterless systems. While air-cooled chillers use no water, they use comparatively more energy.”

15. Sustainable by design: Next-generation datacenters consume zero water for cooling
    Microsoft · 2024-12-09
    Source excerpt

    “Replacement of evaporative systems with mechanical cooling will increase our power usage effectiveness (PUE). … The result is a nominal increase in our annual energy usage compared to our evaporative datacenter designs across the global fleet.”

Each source was opened and checked against the excerpt shown. Company statements are identified as such. Figures are as published; where sources differ, each is shown.