The average desktop computer uses between 60 and 300 watts of electricity, while a laptop tends to use between 15 and 60 watts. The exact usage is difficult to determine, since it depends on the hardware configuration, and these can vary greatly.
The monitor uses approximately 20 to 40 watts. Variables such as the video card and 3D rendering capacity can substantially increase the amount of electricity that is used. Power saving modes can help to reduce the amount of power that a computer uses. Sleep mode, for instance, uses only 1 to 5 watts of power. An electricity usage monitor or power meter can help to determine the exact amount of wattage used by an individual computer system.