Last week, I wrote about measuring the electricity my computer was using by plugging it into an electrical meter called a Kill a Watt.

This week, I decided to try my hair dryer with the Kill a Watt, and holy cow. So my computer was drawing about 92 watts. My hair dryer on low used 402 watts. Switch it to high, and it goes to 1440 watts!

Why is that number so high? Well, the hair dryer is producing heat, and that can consume a lot of electricity. Here’s a great list from the Department of Energy with the typical wattages of many appliances. Some of the big electricity users are obvious: your water heater, your refrigerator, dishwashers. But some of the smaller appliances on the list that are unexpectedly high produce a lot of heat: irons, toasters and hair dryers, for instance.

On the other hand, just because an appliance uses a lot of electricity while it’s on doesn’t mean much, because it all depends on how long you leave it on. Remember, your electric bill is based on kilowatt-hours, and that’s electric use over time. And while I use my computer for many hours a day, I typically spend five minutes or less drying my hair. So where am I using the most electricity?

Hair Dryer vs. Computer: Here’s How It Breaks Down

So, I’ve left the Kill a Watt plugged into my computer for 10 days now, and the meter shows that during that time the computer has used 13.5 kilowatt-hours of electricity.

Have I used that much electricity over the last 10 days while drying my hair? Not even close. 1.5 kilowatt-hours is a better guess, because I've probably spent a total of an hour* drying my hair over the last 10 days.

So, yes, I’m using far more electricity with my computer than with my hair dryer.

Want to do some more math? You can find out how all that translates to greenhouse gas emissions here.

*Update 11/26/08

OK, it's true. An "hour" was just a lazy guesstimate on my part. I didn't really intend to measure how long I spent drying my hair over 10 days with the Kill a Watt. I mean, these numbers are close enough, right?

But now certain family members have challenged whether I really spend only five minutes a day drying my hair. Maybe I'm using a lot more electricity with the hair dryer than what's recorded here. All right, so now it's on. I'm measuring the exact electricity use of the hair dryer with the Kill a Watt for 10 days to prove that yes, the hair dryer still winds up using less electricity than the computer. When I have an update, I'll post it here. Stay tuned!

Update: 1/19/09

Well, I finally finished counting this up, and I'm happy to report that after 10 days of drying my hair, I had only spent a total of 32 minutes with the hair dryer on. The total on the Kill a watt was .68 kilowatt-hours. As expected, that's far less than the 13.5 kilowatt-hours my computer used over a 10 day period. So yes, I use far less electricity drying my hair than I do running my computer.

What's the point of this story? Just that if you're trying to understand how much electricity you're using, you need to know two things: the wattage of an appliance and how long you're leaving it switched on. Low wattage appliances or electronics can surprise you with how much electricity they consume over time.

Photos by Megan Phelps

How much electricity is your computer using right now? It’s surprisingly easy to find out using a simple electrical meter, such as a Kill a Watt. Right now, I have a Kill a Watt hooked up to my PC, and it shows that I’m using 92 watts of electricity.

 Actually, the figure fluctuates, depending on how hard I’m making the processor work at any given moment. But since I plugged this particular meter into my computer 39 hours ago, it’s used about one kilowatt-hour of electricity.  So what does that mean? What exactly is a kilowatt-hour anyway? Here’s a quick review:

• One kilowatt-hour is equal to one kilowatt consumed over one hour. And one kilowatt is equal to 1,000 watts. (For more energy measurements check out this handy chart from the Energy Information Administration.)

• On your electric bill, you’re charged based on the number of kilowatt-hours (kWh) you consume. For the United States, the average cost of one kWh is about 10 cents.

• For even more math fun, you can consider that this one kilowatt-hour is equal to roughly 2 pounds of greenhouse gases, because electricity in the area where I live comes primarily from coal.

So here’s another interesting question: How does my computer compare to other computers? Well, last week we hooked up a Kill a Watt to another editor’s computer, and his laptop was only drawing about 30 watts of electricity. Humph. Oh well, I suppose it’s not a competition.

But the possibilities for measuring and figuring out how to reduce your energy use are endless. For some great ideas, check out this article from Gary Reysa, with his Eight Great Energy Saving Projects. He measured the energy savings of eight different projects and calculated the dollar savings and reduced carbon emissions for each one. You can find even more of these projects on his Web site, BuilditSolar.com.

Photo by Megan Phelps

This week, I've been using a Kill a Watt at home. It's a small meter that costs about $25, and you can use it to measure the electricity consumption of your appliances and home electronics. (There are other meters that do more or less the same thing, including the Watt Minder and the Watt's Up.)

The way it works is simple. For any electrical appliance that you plug into the meter, it can tell you how many watts that appliance is using. Over time, it also adds up the kilowatt hours used, so you can relate that number directly to what's on your electric bill.

Using the Kill a Watt is easy, and it's easy to get a little carried away with it. I measured the energy use of every appliance and electrical gadget in my house, even when it required moving furniture. (Is your refrigerator running? As I write this mine is, and it's using almost 150 watts!) On the other hand, if you're just interested in a ballpark estimate of how much electricity each device uses, you can check out this list from the Department of Energy which has typical values for radios, coffeemakers, DVD players, washing machines and many other common appliances.

Once you've identified the electronics and appliances in your home that are using the most energy, you can target the areas where saving energy will save you the most money. For example, you might decide to start using energy efficient light bulbs, turn on the power saving settings on your computer, or replace inefficient older appliances with newer energy-efficient models.

Have you tried measuring your electricity use at home? Have you found easy ways to reduce it? You can add your suggestions to the comments field below.