To check PC power consumption in Windows, let us assume your PC is powered directly by an AC power outlet. This is most common scenario for most home PCs. In rare cases, users have a high end UPS or additional batteries to extend backup. To understand PC power consumption, we will neglect the second scenario for the time being.
Concerning PC power consumption in Windows, a desktop PC consumes 300 Watts on an average (without the monitor). During boot time, it consumes the most power: around 400Watts. While working normally, it is anywhere between 260Watts to 400Watts depending upon the number and types of applications running. If you are playing games, you are using more power. Multitasking means more computer resources and thereby an increase in power consumption.
PC power consumption during the "idle" state of a computer is around 160Watts. This also doesn't include power consumption of the monitor. Different monitors of different brands, resolution, and type use different amount of power. For example, a Sony17" monitor consumes 90Watts. The power consumption of an LG 17" monitor is 95Watts. If you go down in inches, the power consumption will go down by few Watts. A Sony 11" monitor has a power consumption of around 80 Watts. Also, LCD monitors consume around 35Watts compared to Cathode Ray Tube (CRT) Monitors.
When your PC is in "Sleep Mode," it consumes no more than 70 Watts of power plus 15 Watts for your monitor. The "Sleep Mode" means almost all components of the PC are inactive, hence minimum PC power consumption.
Fast Fact: Many people turn OFF their monitors before leaving the desk. This gives you temporary savings. The monitor needs power to stay warm. The moment you turn it ON, it pulls out all the power you think you saved. It is better to put the entire PC on standby rather than just turning monitor OFF.
The next section takes a look at different power saving options in Windows and helps you decide if you really need them to keep a check on PC power consumption.
Please Note: The above units are approximates and NOT absolutes. PC power consumption varies per the type of components. It is also dependent on the number/type of applications. For example, graphic intensive applications increase PC power consumption.