There is no information on the exact count, but some use Facebook's disclosed power consumption of its data centers for a guideline. According to the company, it consumes about 509 million kilowatt hours annually, while the data center power usage is estimated to be about 58 megawatts. Combined with Facebook’s published Power Usage Effectiveness (PUE) of 1.07, the company conclusively sends 54.27 megawatts to its servers. At 300 watts per server, that would mean about 180,900 servers, according to James Hamilton. If Facebook can achieve the generally assumed 250 watt estimate for Google, the company may run as many as 217,080 servers.
The growth in server numbers is stunning. Hamilton said that the company may have run just 30,000 servers in October 2009, and 60,000 in June of 2010. He also reminded us that Google's datacenters consume a total of 260 megawatts. With a PUE of 1.14, the company provides 228 megawatts to their servers, which would translate to about 1,040,000 servers at the estimated average power consumption of 250 watts per server.