How Much MONEY Can Turning Off That Light (Or Any Appliance) Really SAVE? Kill-A-Watt Review

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If your mom was like mine, you probably got an earful when you’d leave the lights or TV on in a room after you’d left (“we’re not made of money”). Once you had to start paying your own bills, did you ever wonder how much extra that wound up costing you on your monthly electric bill? I know that a big chunk of our bill comes from the air conditioning, but how much of the rest of it comes from things like the dishwasher, refrigerator and computer(s), and how much comes from forgetting to turn stuff off when we leave the room? Up until now we had no way of figuring that out, but then we got this little gadget that actually measures this mysterious figure. It’s called the Kill-A-Watt Electricity Usage Monitor.

The Kill-A-Watt is a small box that you plug into the wall, then plug an appliance (a light, a stereo, etc.) into. It has a digital readout that will measure volts, current, watts, frequency, and power factor. These are all useful for just testing the outlets in your home–you can quickly determine if an outlet is live, and if it’s receiving the correct “quality” of power (is the voltage too low, for instance?). But the real benefit of the Kill-A-Watt is its ability to measure the actual electricity used by whatever you have plugged in.

Electricity is measured in kilowatt hours, abbreviated as kWh. The energy a device uses is measured in watts, and you multiply that times the hours it is turned on to get kWh. For example, a 40-watt light bulb running for 25 hours would use 1 kWh (40 x 25 = 1000).

You can figure out the amount you pay per kWh by looking at your electric bill or logging on to your electric company’s web site. In our area, we pay about 11 cents per kWh (plus taxes and other fees of course), so that’s the figure we’ll use for all our calculations.

The first device tested was my computer. I have a desktop tower, two monitors, an external hard drive, a printer, and various network gadgets. The monitors and the printer will go dark after they haven’t been used for a while, but the computer and the external hard drive are running constantly. I wanted to first see how much it was actually costing us to run all of this, and then if we could really save any money by putting the computer to sleep.

I plugged everything into a large power strip, then into the Kill A Watt. As soon as you turn on whatever is plugged in, the Kill-A-Watt starts recording the kWh used, and the duration (in hours) the appliance is turned on. After running for 12 hours, the meter read 1.03 kWh, which meant it had used right at 11 cents worth of electricity. So that’s less than a quarter a day, or about $80 per year. If I had the computer go to sleep during periods it’s not used, I could probably shave a little off of that, but not much – we use it to store files for other users on our home network, plus it runs backups of the other machines during the night, so there really isn’t much time that it’s truly “idle”. I could probably get that cost down to maybe $50-$60 per year.

Next we tested our Excalibur dehydrator. I expected this to be worse, after all, a dehydrator is really just an electric heater and a fan, and anything that generates heat is going to use a lot of electricity. We ran the dehydrator for 12 hours on a medium setting (about 135 degrees), and determined that it used 3.56 kWh. So, breaking out the calculator, that gives us a cost of 40 cents. We’re not worried about that amount; after all, we don’t run it 24/7, and dehydrating things ourselves is still cheaper than purchasing dehydrated foods, especially if we use all 9 trays at once.

Next it was on to the refrigerator. Most modern appliances come with a tag that tells you the estimated annual energy usage, but we wanted to see how accurate that was. After 12 hours our fridge had used .63 kWh, or about 460 kWh per year. The tag that was originally on it estimated 455 kWh per year (or about $50), so it was pretty accurate. If we had found the reading to be much higher, that might have been an indication that the refrigerator was working harder than it should, and we could either check to see if the temperature was too low, or if the coils needed cleaning.

Finally it was on to the part we were really curious about – light bulbs. All of the new compact fluorescent (CFL) and light-emitting diode (LED) bulbs promise savings over the old incandescent bulbs, but how much money will they really save you?

  • First, we ran an old-school 60-watt incandescent bulb for 12 hours. It used .74 kWh, or about 8 cents of electricity.
  • Next we used a 60-watt (equivalent) CFL bulb for 12 hours. It used .15 kWh, or about 1.7 cents of electricity.
  • Finally we tried a 60-watt (equivalent) LED bulb for 12 hours. It used .11 kWh, or about 1.2 cents of electricity.

So the LED bulb will definitely use the least amount of electricity per year, but you also have to look at the cost of the bulb itself. The incandescent bulb cost $1.90 (and would have been less in a multi-pack), the CFL was $2.50, and the LED was $8. If you ran each bulb for 3 hours per day, in a year the incandescent would cost you $7.43 in electricity, the CFL would cost $1.50, and the LED would cost $1.10. So you can see the obvious cost savings by switching to CFL, but to us it doesn’t seem like LED bulbs are worth it yet. You only save 40 cents a year over CFL, but they cost $5.50 more, so it would take you over 13 years to break even!

My only gripe about the Kill-A-Watt is that since it’s plugged directly into to wall, it can be a bit hard to read the display. Once you unplug it the display goes blank, so you need to take your readings while it’s still connected. If your outlet is behind some furniture or an appliance this can be difficult, but since you’ll probably only be taking one or two readings, this is a minor inconvenience.

We found the Kill-A-Watt to be an interesting experiment, and it convinced us NOT to make a big investment into switching our lights over to LEDs! That paid for the cost of the device right there. There are still several appliances we want to monitor –an electric heater we use in the winter, our TV and DVR that are just on standby most of the day, etc. I hate to sound wasteful, but it also showed us that we didn’t need to be terribly concerned about forgetting to turn off the kitchen light at night – we can afford the 15 cent hit every once in a while. If you want to know without a doubt what devices are the biggest users of your monthly electric bill, this device is perfect. We’d love to see a 220-volt version that would let us see what our air conditioner costs to run, but maybe we’re better off not knowing!

  • Rick Beacham says:

    I see that this is from around 2014… LED bulbs are quite a bit cheaper now… SYLVANIA Ultra 6-Pack 60W Equivalent Dimmable Daylight A19 LED Light Fixture Light Bulbs $19.98.. or $3.33 a bulb.. Sams and Costco frequently run specials where they are even cheaper than this… but, I agree that bulbs are not the real culprit at most homes….

  • Tom says:

    I think that if you evaluate the cost over the lifespan of the bulb and account for inflation, you’ll definitely come to the conclusion that LEDs (which can be had for under $3 at Walmart) are definitely worth the cost. Check out this online calculator to help show how much you can save:

  • Sean says:

    Food for thought from ruler of the empire, Paul Wheaton. Unfortunately, he doesn’t have a lot to say about LEDs.

    CFL Article

  • Jeanne S says:

    CFLs are fluorescent lights, and anyone with chronic migraines should NOT use them! Most people don’t realize that fluorescent lights are one of the most common migraine triggers. If you spend $50 or more per month on prescriptions, supplements, etc to help prevent or treat migraines like I do, having CFLs in your home can easily raise that cost dramatically because the CFLs could be increasing your migraine frequency dramatically! I won’t have them in my house. The dollar store still has plenty of cheap incandescent bulbs available, and buying 2 for a buck means it doesn’t matter if they only last 6-12 months, I still get my money’s worth!

  • Donna says:

    I’m still trying to figure out why LED bulbs are so expensive, yet, I can get flashlights and solar ones for a dollar??

    • Ray says:

      It’s due to the dc transformer in each bulb…an LED runs on DC…in a flashlight, batteries are putting out DC. In a traditional light socket, you have to convert the AC to DC. This requires a power supply (in the base of the led bulb) which, leads to an inefficiency hit which causes heat.

  • Doug says:

    I also have the Kill-A-Watt and it is interesting how much or not you save. Some things just don’t make sense to worry about. I also found the display hard to read when plugged into an outlet. I purchased a 1 foot extension cord from Menards for a couple of dollars. It let’s me read the output much easier.

  • Shirel says:

    We live off grid so using the kill-a-watt serves a much higher purpose. When your electricity comes from solar panels and a battery bank you ABSOLUTELY have to know what every single light and appliance actually draws. Not because of money, but in terms of how much electricity can you use and still have enough to do all the things you need to do. So yes, LED lights are more expensive to purchase, but in terms of how long we can have them on, they are priceless. Anyone who lives off grid knows this. As well as how useful the kill-a-watt meter truly is.

  • Allison K says:

    There are two advantages to LED’s over CFL’s. The first is that if you ive in an area where the power grid is low voltage or not stable, CFL’s will only last 6-8 months. The second is disposal, as CFL’s are still flourescent, and have mercury in them. There is even talk about banning CFL’s because of this. It is already illegal to take them to a landfill, you have to pay for their disposal.

  • Mensa141 says:

    An Electric dryer is an eye popper. I don’t have a 220 volt kill-a-watt either but I can check my daily usage via the web at my electric company. On the days we do laundry, usually three loads, we double the amount of electric consumed which includes air conditioning.

    If someone can measure the amount of electric consumed drying a normal electric drying cycle it would be much appreciated.

    • JR says:

      The two biggest culprits of energy use are an electric water heater, and a central a/c unit. In areas where a significant portion of the year require a/c (far southern states, southwestern areas), a/c can easily be 1/2 of the overall expense.

  • Noah North says:

    LED lights aren’t exactly safe (“Hidden Blue Hazard? LED Lighting and Retinal Damage in Rats.” March 2014. and “Do ‘environmentally friendly’ LED lights cause BLINDNESS?” May 2013. And, CFL lights aren’t much better (“Mercury in Compact Fluorescent Lamps.” 2010. and “Cleaning Up a Broken CFL.” June 2014. If incandescent lights can last months before burnout, I believe that a few dollars buying and operating them for a year isn’t an extravagance, especially considering the risks involved with the alternatives.

  • Rebecca says:

    I had changed most of my bulbs to CFL because certain ones were hard to get to and CFL was supposed to last longer. I marked them with the month and year so I new how long they lasted the second round of bulb changes. All lasted years short of how long they were supposed to. I got three years out of a five year bulb pretty consistently. When I ran out of those I quit using them and went a head and invested in the LED bulbs. They are lasting and lasting. The down fall with them is they are not approved for closed fixtures. They do get hot so I only put them where they are approved to go in open fixtures. I decided it was worth it not have to have to change bulbs as often. My husband says the LED will last way longer than anything else and it is not a toxic bulb that has to be disposed of any special way. That was one of my major complaints about CFL bulbs. Another problem I found with the CFL was it didn’t fit in all the fixtures because it is to large.

  • Terry says:

    You can get a 220V version from JLB Electrical in the UK, cost me around US$30 with shipping to South Africa.

  • Sabrina says:

    This is really fascinating actually. Thank you for passing on the information AND your discoveries! I am curious to know how one can measure the usage for ceiling fans or anything else that is already installed into the wall or ceiling. If I wanted to figure out the usage for the dryer or washing machine, I would assume that I would figure out the numbers for one load and then multiply it to the number of loads per month – sound right? I think I will have to look into getting one of these! Do they have one for calculating the amount of water that is used? Thanks again!

  • Christopher de Vidal says:

    “My only gripe about the Kill-A-Watt is that since it’s plugged directly into to wall, it can be a bit hard to read the display.”

    Solved with an extension cord.

  • PJ says:

    I once left all of our basement lights on after going to sleep, my wife got upset and told me I was wasting money. I ran the calculations and came up with something like 8 cents to run the lights all night. 8 CENTS….might as well be zero.

  • Mike the Gardener says:

    While it looks like your numbers are pretty accurate, did you take into account the number of hours a light bulb can run for?

    While I don’t believe LED technology is quite there yet, it is making strong gains.

    Incadescents also burn hotter as do halogens, where as LEDs generate virtually no heat.

    I am not saying we should change out all bulbs to LEDs or, God forbid, force people to use them, but they are making gains and I believe in the next 10 years will be the industry standard. We shall see.

    • Bill Osuch says:

      True, a CFL or LED will probably have a longer lifespan, although we’ve had CFLs that burned out before incandescents. Many CFL and LED bulbs come with some of warranty as well, if you’re able to keep up with all the paperwork.

      We’ve changed out most of our bulbs to CFLs (except for ceiling fans, they tend to flicker); I just don’t think LEDs are at the price point yet where it’s worth making the switch from CFL.

      • Tim says:


        Loved the article. Very informative!

        We attempted the CFL route in our living room, and it was “OK” for most of our lights. The problem we found were with “dimmer” type lights. With many 45W light bulbs in that one room, we saw a healthy drop in our monthly electric bill when we swapped to CFL.

        I agree that LED light bulbs can be quite expensive, and I’m still not ready to believe that these are going to last as many years as they promote. Price really depends on where you find them. We made a trip to IKEA with our kids when they were shopping for our grand daughter’s crib. While in the lighting section, we found LED lights for about $4 each. On a whim, we converted a few lights to the LEDs and found that they were actually brighter than the equivalent CFLs. Additionally, the light was more crisp and white. Things were actually clearer. That caused me to take a second look at LEDs. When we found 3 pack LEDs at Costco for $20, we decided to convert the rest of our lights to LED. That cost me roughly $60. I then placed some solar LED lights on our barn and garage. This allowed us to turn off a big “street light” type light in our driveway. Running this way, we’ve now seen a significant drop in our electric usage. Our latest bill dropped by almost 100 Kwh. We’ll see what next month brings. Meanwhile, I’ve already saved most of what I spent on the LEDs.

        While I’m not 1000% sold on LEDs yet, there have been some nice advances! Still not the best for dimmer type situations, but……

        • Roy Parker says:

          I have converted several lights to LED including an under cabinet pair of led strip lights that have individual switches (burn one or both). They are expensive but they run cheaper and another benefit is they do not emit as much heat as a cfl. You can burn the led for hours and still hold it in your bare hand.

          • Bill Osuch says:

            Yup, we’ve got a mixture of CFL and LED lights in the fixture above the bathroom mirror – you can hold your hand on the LEDs after they’ve been on for an hour, but not the CFLs!

      • Mike the Gardener says:

        I have had CFLs burn out before incandescents as well .. I dont even use CFLs, unless I absolutely can not find an LED or Incandescent … to me CFLs are worthless … but that’s me. Others may disagree.

      • gene says:

        Several months ago i was forced to replace the two 150 watt incandescent bulbs over the work end of my garage with 300watt CFLs. The biggest problem was i could no longer see to work on my vehicles or the bench. Since i could not find any 150 watt incandescent bulbs i had to add three two foot two bulb fixtures to get the same amount of usable light.

    • Keith says:

      I would strongly urge you to spend the money and buy the LED BULBS! I too have a kill-a-watt meter. One thing your hours long test did not account for is how terribly inefficient a CFL is during start up because they do not provide their full light output until they are warmed up which can take several minutes. LED’s are at max light output as soon as they are switched on. We made a mass change of the most often used bulbs in our house and saved over $30 in the first month. Most of these LEDS have a 20 plus year life span and are not a health hazard like a CFL which contains mercury.

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