Calculate your PC's energy use

Microsoft's free Joulemeter utility gives you a rough estimate of a Windows system's power consumption. Plus: tips for reducing your electronics energy bill.

Dennis O'Reilly Former CNET contributor
Dennis O'Reilly began writing about workplace technology as an editor for Ziff-Davis' Computer Select, back when CDs were new-fangled, and IBM's PC XT was wowing the crowds at Comdex. He spent more than seven years running PC World's award-winning Here's How section, beginning in 2000. O'Reilly has written about everything from web search to PC security to Microsoft Excel customizations. Along with designing, building, and managing several different web sites, Dennis created the Travel Reference Library, a database of travel guidebook reviews that was converted to the web in 1996 and operated through 2000.
Dennis O'Reilly
3 min read

Microsoft Joulemeter power-measurement utility
Microsoft's free Joulemeter utility calculates the energy use of a Windows PC Screenshot by Dennis O'Reilly/CNET

According to Michael Bluejay, who also goes by Mr. Electricity, it costs from $631 to $5.50 per year to power a PC.

Even Mr. Electricity admits that's quite a range. A more typical annual energy bill for a Windows desktop PC that uses an LCD monitor and has sleep mode enabled is less than $10.

Microsoft's free Joulemeter program lets you calculate the power used by a Windows desktop or laptop. Joulemeter's developers intend the program to be used in conjunction with an external power meter when measuring a desktop's energy consumption, although the program's Manual Entry option generates an approximate power-usage number; the energy use of laptops is determined without requiring an external power meter.

For precise calculations of desktop power consumption, the Joulemeter user guide indicates that a WattsUp Pro power meter is required. WattsUp meters cost from $96 to $196 on the vendor's site.

The program also estimates the amount of energy being used by each application currently running. Enter the name of the program's executable file (such as "firefox.exe") in the text box under Application Power on the Power Usage tab and click the Start button. You can also save the current readings to a file for future reference.

Joulemeter Application Power calculation
The Joulemeter power-measurement utility calculates the energy used by specific applications. Screenshot by Dennis O'Reilly/CNET

When I used Joulemeter's manual approach to estimate the energy consumed by two Windows 7 desktops and a Windows 8.1 laptop, the utility indicated that the desktops used about 75 watts an hour and the notebook about 25 watts an hour. Since our local power company charges an average of just more than 15 cents per kilowatt hour, our household's computer energy bill is in the vicinity of $1 a month.

Of course, this figure doesn't include the cost of powering our two iPhones and three tablets. In September 2012, Outlier's Barry Fischer calculated the cost of charging an iPhone 5 and a Galaxy S3 for one year at 41 cents and 53 cents, respectively. In a post from June 2012, Don Reisinger reported that an iPad's annual energy bill comes to $1.36, according to a study conducted by the Electric Power Research Institute.

No matter how you slice it, that's a lot less juice consumed by our gadgets and computers than is used by other household appliances. According to Mr. Electricity's TV energy use calculator, a 46-inch Samsung LCD TV that is watched an average of 5 hours a day runs up an annual energy tab of just under $47. That's the equivalent of 537 pounds of CO2 pumped into the atmosphere, according to the calculator's figures.

A little energy conservation goes a long way

In the spirit of upcoming Earth Day, here are a handful of ways to minimize your household energy use.

Sleep mode saves time, money, and the environment.

According to the U.S. Environmental Protection Agency's EnergyStar FAQ, using your computer's power-saving modes can save you up to $50 a year. I don't know where the EPA got that figure, but it's clear using less energy saves much more than money.

On the How-To Geek site, Chris Hoffman explains the differences between Windows' Sleep, Hibernate, and Shutdown modes. Unfortunately, sleep mode often causes more problems than it solves. The Microsoft Support site provides potential solutions to many sleep-mode glitches.

Turn off power at the source.

The Green Options site offers tips for reducing "vampire" power, which is the energy drained by devices that are "off" but still plugged in. Among the tips are to unplug chargers when you're not using them, switch off power strips, and use "smart" power strips. In a post from last week, Ry Crist described the Quirky Pivot Power Genius, one of the new products from home-automation vendor SmartThings.

The various power modes of modern electronics make it difficult to determine exactly when a device is "off." The American Council for an Energy-Efficient Economy (they could save some energy by coming up with a shorter name) explains the power modes of home electronics and offers advice on what to look for when shopping for energy-efficient appliances and devices.