Determining how much electric power your PC is consuming is very difficult because the power consumption of various hardware components keeps varying with time. For example, the power consumed by your screen goes up if the brightness of your screen goes up. If you want to know how much electric power your PC is consuming at any given time, then you can make use of the free Joulemeter tool. This tool is developed by Microsoft Research and it can estimate the power consumption of your PC. It tracks computer resources, such as CPU utilization and screen brightness, and estimates power usage.
The Joulemeter tool can run on laptops which are powered by battery without requiring any extra hardware. But if you want to use Joulemeter on a desktop PC, then Microsoft recommends a wattmeter with USB connection. You can hookup this wattmeter into your computer using a USB cable and it is needed only for a few seconds. However, the Joulemeter software can work without any wattmeter as well, only the power consumption estimatation will not be very accurate.
After installing the Joulemeter application, you can start it from the Start Menu (or Start Screen in Windows 8). You have to select a calibration setup from the drop down menu and then click on the Perform Calibration button. If you have a desktop PC and you do not have a USB wattmeter, then you can manually enter a power model by clicking on the Manual Entry button. Try to be as precise as possible while entering the power model entries manually.
In a short while after clicking on the Perform Calibration button, the Joulemeter would display the power consumption usage in Watts. The report consists of power consumption by your CPU, monitor, hard disk and base (base power means power used by your PC even when its idle). All the numbers are in watts. The total of power consumption is also shown.
You can use the data provided by the Joulemeter application to realize how much power your PC is consuming everyday. By knowing the average power consumption of your PC, you can estimate the cost of electric power consumption for your office or organization where multiple computers are being run. This can also let you plan a stratergy or make hardware changes to cut down your electric power costs.
You can download Joulemeter from http://research.microsoft.com/.