How much energy on average does an office use?

Across the United States, the average annual energy intensity for office buildings is 79.8 kBtu(Kilo British Thermal Units, 1kWh=3,412 Btu) per square foot (11 square feet=1 square meter) and the average cost is $1.65 per square foot. Of the total energy consumption, 66% is for electricity and 34% is for natural gas and other fuels. This translates to 15.5 kWh per square foot of electricity and 0.27 therms per square foot of natural gas.
As show in Figure 2, space conditioning and lighting together account for 70% of all energy consumed in a typical office building, with an additional 20% of energy consumption used to power office equipment. The remaining energy is consumed by water heating, cooking, and refrigeration systems, as well as other miscellaneous uses.

Source:
http://www.epa.gov/solar/documents/sector-meeting/4bi_officebuilding.pdf