Kill-A-Watt, WolframAlpha, and the itemized electric bill

I’ve always imagined getting an itemized electric bill. We’re not there yet, but when I saw a Kill-A-Watt at Radio Shack last night I remembered the discussion thread at this 2007 blog post and impulsively bought it.

In a way I’m glad I waited until 2009 because a companion tool is available now that wasn’t then: WolframAlpha. Its fluency with units, conversions, and comparisons is really helpful if, like me, you can’t do that stuff quickly and easily in your head.

So, for example, I’m sitting at my desk with the Kill-A-Watt watching my main power strip. I have a mixer here that I use about an hour a week for podcast recording. There’s no power switch because, well, why bother, just leave it on, it’s a tiny draw. Negligible.

I reach over and unplug it. Now I’m drawing 9 fewer watts. But what does that mean? I consult Wolfram Alpha:

Q: 9 W

A: About half the power expended by the human brain.

On a monthly basis?

Q: 9 W * (30 * 24 hours)

A: About half the energy released by combustion of one kilogram of gasoline.

In gallons?

Q: ( 1 kilogram / density of gasoline ) / 2

A: Less than a fifth of a gallon.

Relative to my electric usage, which was 1291 kWh last month?

Q: 9 W / (1291kwh / ( 30 * 24 hours)) * 100

A: Half a percent.

In dollars?

Q: 9 W / (1291kwh / ( 30 * 24 hours)) * $205.60

A: One dollar.

I find these comparisons really helpful. A dollar a month is a rounding error. But if I think of it as the energy equivalent of driving my car 7.2 miles, that makes me want to reach over and unplug the mixer for the 715 hours per month I’m not using it.

Saul Griffith has internalized these calculations, but most of us need help. A next-gen Kill-A-Watt that did these sorts of conversions and comparisons could be a real behavior changer.

29 thoughts on “Kill-A-Watt, WolframAlpha, and the itemized electric bill

  1. This is excellent, John, not only for ‘visualizing’ energy use, but for exploring ways to use W|A. There’s a lot of untapped power there. (No pun intended).

  2. It also makes me wish we could manage this through the Distribution Panel. I think circuit breakers could be made smart enough to take out whole circuits on a timed basis. Utilities can manage some amount electricity distribution centrally and we need the same capability on the level of the ‘house’. I would bet that most houses currently wired for 200Amp service could drop to 100Amp service if the distribution panel were ‘smarter’ somehow. But we’re still operating under the old think of ‘peak load’.

  3. A similar device (the Wattson by diy kyoto– has had a more “approachable” interface from its inception. The supporting software provides the long-term analysis and trend reporting, but I agree it would be interesting to see saving expressed in alternate ways, if only to make people stop and think. No associations with diy kyoto other than as a satisfied customer/user …

  4. Energy costs are higher here (UK), the market has only recently been exposed to competition for supply, so I guess there is also a newish culture of change.

    Certainly there is a growing awareness of consumption and the green issues of energy consumption, recycling, etc are getting much more prominence in day-to-day life. We don’t have the abundance of resources that the US (believes it?) has, nor the vast markets to defray costs over …

  5. Although the visualizations and equivalences are nice, what really needs work is being able to collect the data inexpensively — $150 for a TED device is ridiculous if you already have a computer (or router) at home that is on all the time — the cost of two 100Amp Current Transformers plus the circuit board (TINI ?) that could be polled from the computer to collect usage and send it on to Google Power Meter or something like that should be less than $50, but no one is making that…maybe now that I’ve said it I will :-)

  6. I whole-heartedly agree … interestingly, diy kyoto seem to have acknowledged that their latest tools are a little clumsy in places and have decided to open up their API for developers. Not had the opportunity to follow it up yet, but as their hardware is stable, their access is USB and cross-platform API is available then it offers potential.

    We’ve also got some similar offerings over here tying into Google PowerMeter, so I’d guess they are starting to feel the limits of being a small team who whilst they were early to the scene have many snapping at their heals (AlertMe, first:utility).

  7. The job isn’t done when you’ve sealed your windows and switched to CFLs.

    Absolutely not.

    In theory, though, a citizenry that has gone through those residential exercises will be more likely to press for change in the commercial, industrial, and transportation sectors.

  8. Do you need something complicated to make a dent in user behavior?

    Automobiles with real time gas mileage meters show one number (miles per gallon) and drive a whole world of people doing “hypermiling” to get the number as high as they can.

    I’d suspect that a similar single-output measure (instantaneous whole-house kilowatts) would have you or me scurrying around to turn off things if the number was too high, and to better understand what the normal was at noon or at 11 pm. And I don’t think it has to be plugged into a 24×7 computerized monitoring system to be effective in changing behavior any more than your car has to provide a perpetual memory of its gas mileage in order for you to drive differently.

  9. I’d suspect that a similar single-output measure (instantaneous whole-house kilowatts) would have you or me scurrying around to turn off things if the number was too high

    Yes, that’s what the UK devices mentioned here do. In certain cases you’d also want a per-appliance monitor — notably the fridge, so you’d know how its efficiency is decaying.

    Crazy that we don’t have these yet in the US.

  10. According to WA it’s 1.3x an average US household.

    Sincee we’re running my home office and my wife’s art studio on the same meter as the household, and we’re here almost all the time, it’s arguably not out of bounds.

    Still, your reaction is instructive in several ways.

    First, I’m certain that the average for a European household is lower, and I’d be interested to see the country by country data if anyone can point to it.

    Second, I’m struck by the fact that you evidently have an intuitive sense of what 1291kWh means. I really didn’t until I went through this exercise. It seems to me that when Americans discuss our power use, we talk in terms of dollars, a somewhat loosely-coupled measure given the elastic price of power. We have not learned to think in units of power.

    1. Well, I double checked my calculations of my home consumption twice, and then I looked for documentation: a Portuguese household averages around 380kWh monthly (link:, so even by USA average we are WAY lower (mine averages 275, but we make sure we save the most we can.)

      1. We know, of course, that the American lifestyle is based on conspicuous consumption of energy. But we rarely if ever make this kind of direct comparison.

        It would be fascinating to compare a US to a UK or European household in a more detailed way. How much of US power consumption is related to:

        – Electronics

        – Aging appliances (clothes dryers, fridges) that we have too little incentive to replace

        – Categorical differences. Our friends in Wales, for example, use neither a dishwasher nor an electric clothes dryer.

        – Size of dwelling.

    2. In Holland the average energy consumption per household is 3500 kWh elektricity per year. Plus 2000 m³ natural gas per year.
      Of course if you would have a home office + a studio it would be higher.
      Our house is very much energy optimized. I just received my yearly overview and in the past year I used 3300 kWh. That is all the energy the house uses, including heating (so no gas). Besides this is all green electricity, so no carbon footprint.
      I am kWh-aware because I have noted my monthly meter values most of the time I was a home owner.

  11. I suppose we keep below the national average because we use neither electric dishwasher or clothes drier and we only have a couple of laptops. Still, we use a lot of butane/propane for cooking/water heating, which brings the bill a bit down as well, and I guess the majority of Portuguese households still do, although there’s a tendency to go towards electric the last few years.

  12. Pingback: brain power
  13. I love my Kill A Watt. Knowledge is power, and it’s saved money on my utility bills. To take the measurements into $$$ terms can be a pain, so I made a simple webpage calculator to make it easy for me.. anyone can use it at

  14. As a matter of fact, he was pretending to be ill.That makes no difference.Just around the comer.His words are strongly impressed on my memory.I was late for work yesterday.Long ago, people believed that the world was flat.Long ago, people believed that the world was flat.15 divided by3 equals 5.It rather surprised me.Will you connect this wire to the television ?

Leave a Reply