A Quick Way to Estimate Energy Consumption

We all know that using more energy means paying more money. But, even I (a math guy) find it hard to quickly calculate how much a device costs to run. So, I devised some quick do-it-in-your-head estimating techniques that can help. I used an electric cost of between $0.12-$0.13 / KWh for these estimates (pretty typical across the U.S. right now). If you pay substantially more or less, these equations should be adjusted. Even with slight errors, these equations give a good reference basis to work from when you’re deciding whether to plug in.

Estimating Equations

#Amps / 3 = $Dollars Spent Per Day (assuming 110 voltage)
(e.g. a 15 Amp space heater running all day will cost ~$5.00 dollars because 15/3=5).

#KW * 3 = $Dollars Spent Per Day (regardless of voltage)
(e.g. a 1000 Watt (1 KW) Heat Lamp running all day will cost ~$3.00 dollars because 1*3=3).

Some Useful Examples

1000 Watt Heat Lamp = $3.00 Per Day / $90/month
100 Watt Incandescent Bulb = $0.30 Per Day / $9.00/month
23 Watt CFL Bulb = $0.06 Per Day / $1.80/month
30 Kilowatt Electric Furnace = $10.00 Per Day / $300/month (scary, eh?)
15 Amp Space Heater = $5.00 Per Day / $150/month

Limitations of These Estimators

Rember, most items in your house don’t run all day (furnances cycle on and off; you turn off lights when leaving the room) so aggregate numbers can be misleading. You should adjust the resulting numbers by the percentage of the day you expect something to actually draw energy.

What do you think? Do you use some other way to quickly estimate energy cost?