This study estimates the electricity used by data centers worldwide and regionally, based on more detailed data than previous assessments. It finds that global data center electricity use doubled from 2000 to 2005, with three-quarters of this growth attributed to the increase in volume servers. Data center communications and storage equipment each contributed about 10% of the growth. The average annual growth rate was 16.7%, with the Asia Pacific region (excluding Japan) being the only major region with growth significantly exceeding this average. In 2005, data center electricity use represented about 0.5% of total world electricity consumption, or 1% when including cooling and power distribution. Worldwide data center power demand in 2005 was equivalent to about seventeen 1000 MW power plants. The US and Europe accounted for about two-thirds of total data center electricity use, with Japan, Asia Pacific (excluding Japan), and the rest of the world each accounting for 10-15%. Asia Pacific (excluding Japan) grew at a 23% annual rate, reflecting significant economic growth in China, India, and other Asian economies. The Asia Pacific region was the only major region with data center electricity use growing at a rate significantly greater than the world average. Europe also grew slightly faster than the world average over this period. The study forecasts that data center electricity use will grow by 76% from 2005 to 2010, leading to an average annual growth rate of about 12%. Future work includes more accurate characterization of the installed base of equipment by region, more accurate characterization of cooling and infrastructure efficiency, more detailed segmentation of the server markets, and opportunities for efficiency improvements. The study highlights the importance of data center electricity use and the need for accurate data to inform policy and business decisions.This study estimates the electricity used by data centers worldwide and regionally, based on more detailed data than previous assessments. It finds that global data center electricity use doubled from 2000 to 2005, with three-quarters of this growth attributed to the increase in volume servers. Data center communications and storage equipment each contributed about 10% of the growth. The average annual growth rate was 16.7%, with the Asia Pacific region (excluding Japan) being the only major region with growth significantly exceeding this average. In 2005, data center electricity use represented about 0.5% of total world electricity consumption, or 1% when including cooling and power distribution. Worldwide data center power demand in 2005 was equivalent to about seventeen 1000 MW power plants. The US and Europe accounted for about two-thirds of total data center electricity use, with Japan, Asia Pacific (excluding Japan), and the rest of the world each accounting for 10-15%. Asia Pacific (excluding Japan) grew at a 23% annual rate, reflecting significant economic growth in China, India, and other Asian economies. The Asia Pacific region was the only major region with data center electricity use growing at a rate significantly greater than the world average. Europe also grew slightly faster than the world average over this period. The study forecasts that data center electricity use will grow by 76% from 2005 to 2010, leading to an average annual growth rate of about 12%. Future work includes more accurate characterization of the installed base of equipment by region, more accurate characterization of cooling and infrastructure efficiency, more detailed segmentation of the server markets, and opportunities for efficiency improvements. The study highlights the importance of data center electricity use and the need for accurate data to inform policy and business decisions.