What Do I Get For My Kilowatt?

I’m staring at a record of electricity bills over the course of two years, and while it tells me how many kilowatts of electricity were used in each two month period of time, I have no idea how to translate that into any kind of day-to-day practical usage.

So I’ve got a couple of questions. First, what do I get for my kilowatt? In other words, will one kilowatt run my refrigerator for an hour/day/week? How 'bout lights and tv?

And second, has anybody ever figured out what the average kilowatt use per person is? I know about average water usage, because I live in drought country, and there’s always a big discussion about the average number of gallons used by a person daily. Is there anyplace to find out that same information for electricity?



Good utilities will sometimes be able to answer these questions for you. They’ll be able to tell you things like, unless you have a really large house, a space heater won’t save any power since space heaters are so much less efficient than central heating.

If there is a phone number on your power bill, you might give it a call and ask them how many kilowatt-hours it takes to make a slice of toast or take a hot bath. If you have electric heating, they can tell you about how much it saves to improve insulation and caulking.

By the way, kilowatt is a measure of power. When you turn something on, it will run at a certain number of watts which probably won’t change over time. You might also want to ask about energy, usually measured in kilowatt-hours, but it also could be measured in kilowatt-seconds, calories, Calories, etc. So kilowatts are analogous to the speed of a car; kilowatt-hours are analogous to the distance the car has travelled. So you’d ask “How many watts does my fridge consume?” but you might also ask “How many watt-hours does my toaster consume to make a piece of toast.”

A 100w bulb will use a kilowatt in 10 hours. Your 600w baby microwave will use a kilowatt after 1 hour and 40 minutes. You should be able to find the wattage for your stove, oven, refrigerator, washer, dryer (BIG TIME, if electric), and dishwasher somewhere on each appliance, (same with TV, stereo, VCR, etc.). Divide wattage into 1000 to find usage per kilowatt hour.

Aside from direct heat (clothes dryer, stove), the biggest users of electricity are usually motors (fans, etc.). Lights have gotten pretty economical.

I don’t know what “typical” usage is either by household or by person. (My house (electric dryer, lots of heat lamps and hot rocks for reptilian pets) uses way more than I like.)


A watt is a measure of rate of energy usage.

It is equal to one “joule” per second. A joule (J) is a quantity of energy whose definition escapes me at the moment.

Thus, my hair dryer, which says 1400 watts, uses electricity at a rate of 1400 joules per second.

Total quantity of energy is something different. This is where the joule comes in, and where we can start to answer such questions as, “How much energy does my toaster use to toast two slices of bread?”.

If the toaster used energy at a rate of 500 watts for two minutes, it would be 500 W x 120 s = 60 000 joules!

Most North Americans are not used to seeing their energy measured in joules; watt-hours are more common.

But a watt-hour is simply the total amount of energy you use when you use energy at a rate of 1 joule per second for 1 hour.

This equals 1 J/s x 1 h, or 1 J/s x 3600 s, or… 3600 joules!

So the toaster would have used 60 000 joules / 3600 joules/watt-hour = 16.67 watt-hours of electricity. Boris B, you’re right on the mark.

So, tomndebb, a 100-W bulb uses energy at a rate of 100 watts, or 100 joules per second. In one hour, it uses a total of 1 watt-hour, or 3600 joules, of energy.

With a single 100-W bulb, after ten hours, you would still be using energy at the same rate of 100 watts, but you would have used 10 watt-hours, or 36 000 joules, of energy.

It would take ten bulbs to use energy at the rate of 1000 watts, and after just one hour, they would have used 10 watt-hours of energy.

But you’re right–anything that uses electricity to heat (dryer, toaster, etc) will take a lot of power. Some friends of mine had to move out of an electrically-heated house; they literally could not afford the bills (~$600 per MONTH in the winter).

Those of us who are planning a solar-powered house have to be very aware of this kind of thing…

A kilowatt hour is 1000 watts of power used in one hour. The 100 watt bulb thing in Sunspace’s post.

For the science elete out there. Please convert this into how many electrons per hour Melin gets to use for her money.

Remember the electrons are only barrowed and have to be returned to the power company through the ground.

Unless they are AC, in which case you pay for the same electrons over and over again. We did this in Great debates, where someone did not believe in electricity.

I appreciate all this, guys, but it’s the practical stuff I need, not the academic. I have surfed manny websites involving electricity today, and still can’t figure out what it is I need to know, although I’m getting closer.

What it is, is that I have a case where the question turns on whether this woman and her child were living in an apartment, or living at home with her parents. She admits that she kept the apartment, but says that she used it “to be alone” maybe 10 per cent of the time, spending the remaining 90 per cent at mom and dad’s. I wanna know if the usage I’m seeing on her electricity bills for the apartment is consistent with that, or is consistent with them living at the place (one bedroom apartment) on a regular basis.

The other stuff is more interesting, I’ll admit that!


Have you asked the landlord yet? He should have at least a general idea of the utility costs, because people ask about that when they’re apartment-hunting. Also, the landlord is responsible for utility payments while the apartment is vacant, so he might have an idea of how much electricity the place uses up with no people in it.

If that fails, try calling the power company. They can probably tell you the average energy usage for an apartment of that size. Depending on how much statistical data they keep, they might also know how much the usage will drop when the place isn’t occupied all the time.

Laugh hard; it’s a long way to the bank.

I’m not about to challenge Sunspace on the technical end of this question. I had assumed that you wanted to know how you would be billed.

Based on the following quote from the U.S. Department of Energy, I think my calculations come close.


I would think that if it is an apartment, the landlord could put you in contact with other tenants to find out what their bills are. If it is a house or a set of rooms in a house, this would be harder to establish a baseline. (Can you get/subpoena the utility to provide their bills for the period when the woman was living there vs when she was only “going there to be alone”?) Heck, is the woman willing to provide her bills for the before and after periods?

Old appliances might mask her presence (old inefficient heater+fridge+water heater could consume enough energy, running constantly, to overwhelm lightbulbs and stereos), but if you have the wattage for those appliances, you can figure their max, subtract it, and see how many lights she had on “when she wasn’t home.”

I suspect you will be safer getting the bills for the people next door.


Just some rough figures but maybe this will help. If someone were actually living in an apartment they would use:

The television, microwave, dishwasher, stove, lights, hot water heater, radio or stereo, hair dryer.

Other appliances, like the refrigerator and the heat would probably be on whether they were actually there or not, which is unfortunate because they’re a couple of biggies. The heat would probably be turned down and the fridge wouldn’t be opening and closing so there would be some savings, tho.

On a typical day (with guesses for wattage) I’d say the above list would consume – ummm – about 8 to 10 kilowatt-hours per day. Assuming it’s summertime so that electric heat isn’t a factor, and (guessing) maybe 5 kw-hrs a day for the fridge.

If these figures are close then an empty apartment (just the fridge) should use 30 x 5 = 150 kw-hrs. An apartment occupied 10% of the time would use an additional 3 x 10 = 30 kw-hrs for a total of 180 kw-hrs. An apartment occupied full time would use an additional 30 x 10 = 300 kw-hrs for a total of 450 kw-hrs.

I’m nowhere near my power bill so I have no way to check these figures but it might give you some idea about whether or not you have a chance of figuring out whether this person is truth-telling or not.

p.s. I learned to estimate from my heat transfer professor for whom everything was either 1, 2, or 5, or some decimal multiple thereof. Pi, for example, was 5 in his class.

Strangers have the best candy.


Did the person in question ever live with her child in the apartment full time before the time she claimed to live with her parents?

If so, couldn’t you just subpoena her power bills from the power company over a period of time both before and after she claimed to have moved out and compare?

Plunging like stones from a slingshot on Mars.

Melin, I think the place you want to go is a site run by SCE Corp. (The old So. Cal. Energy).

Try here and, if you don’t mind entering your client’s data into a public database, you should get a pretty good idea of what was happening in the apartment.

Livin’ on Tums, Vitamin E and Rogaine

A joule is the amount of energy required to provide one Newton through a length of one meter.

A Newton is the force required to accelerate one kilogram at a rate of one meter per second per second.

That said, I think the electric company is ripping me off because my refrigerator just sits there all day. And don’t get me started that television.

Then…what are Newton’s Joules?


Typer :slight_smile: