How to Calculate the Power Consumption of a Desktop Computer
Your home computer may be a significant component of your monthly electricity bill, may use relatively little power or may be somewhere in between. You can estimate your computer energy consumption using manufacturer guidelines, or actually measure your computer's energy use with third-party devices or your home's own energy meter.
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Instructions
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Estimate
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Understand that the watts indicated on the labels on the computer or power sources are the maximum, not necessarily a representation of actual power used. This number fluctuates.
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Determine the energy requirements for your desktop tower/CPU. Your computer will be labeled with the maximum watts that the computer can use. Your computer manufacturer may publish the energy profiles for its computers on its website, or may send you this information upon request.
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Determine the energy requirement for your monitor, assuming it is not integrated into your desktop. CRT and LCD monitors have very different energy requirements. A 17-inch CRT monitor typically requires 80 watts, whereas a 17-inch LCD only requires 35 watts. The manufacturer of the monitor, either CRT or LCD, also matters. A Macintosh 17-inch CRT, for example, only uses 63 watts, whereas the average 17-inch CRT requires 80 watts.
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Determine energy use for any accessories you may use. These accessories may include wireless keyboards, a wireless mouse, and/or speakers and subwoofer. Again, look to the manufacturer for more information regarding energy output for accessories. For wireless devices, be sure to consider the energy drain to the computer via the USB drive and the batteries in the wireless half of the device.
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Determine your average computer use. High energy demands include faster processors, older processors, being online and heavy use (all drives are in use or the processor is working intensely). Lower energy is demanded by computers in sleep or standby, with newer and/or slower processors, running light programs (word processing) or operating offline. In general, Macs take less energy than PCs, and laptops require less energy than desktops.
Measure & Calculate
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Purchase a watt-hour meter. These energy meters are plugged in-between your device and the wall to measure the use of the appliance. The wattage is then displayed on an attached LCD screen. There are a number of these products available for purchase online, including KillAWatt. More information is available at smarthome.com/9034/Kill-A-Watt-P4400/p.aspx
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Find an online tool to measure your overall home's electricity requirements. Whole systems include products such as The Home Energy Detective, at theenergydetective.com. Different companies offer different products, including Google, which offers the Google PowerMeter. More information is available at google.org/powermeter/howitworks.html.
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Monitor the changes in the electricity requirements for your device by investigating your electricity meter on the side of your house. This method varies depending on whether your meter is analog or digital. Full instructions for either of these methods are available on the Michael Blue Jay site cited below. This method is tedious, but is also free.
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Tips & Warnings
The government now hands out "Energy Star" ratings to computers. More information about this program is available online at energystar.gov/index.cfm?fuseaction=find_a_product.ShowProductGroup&pgw_code=CO.
A computer only uses less energy when the screen is turned off, not when a screensaver is in place. A screensaver uses the same amount of electricity as if the screen were on and in ready status.
