What the heck is a kilowatt hour?
A kilowatt hour (kWh) is a measure of how much energy you’re using. It doesn’t mean the number of kilowatts you’re using per hour. It is simply a unit of measurement that equals the amount of energy you would use if you kept a 1,000 watt appliance running for an hour.
Before we see how much electricity costs, we have to understand how it's measured. When you buy gas they charge you by the gallon. When you buy electricity they charge you by the kilowatt-hour (kWh). When you use 1000 watts for 1 hour, that's a kilowatt-hour. For example:medium window-unit AC | |||
large window-unit AC | |||
small window-unit AC | |||
42' ceiling fan on low speed | |||
light bulb | (i.e., all month) | ||
CFL light bulb |
To get kilowatt-hours, take the wattage of the device, multiply by the number of hours you use it, and divide by 1000. (Dividing by 1000 changes it from watt-hours to kilowatt-hours.) That's exactly what I did in the table above. If you'd rather not do the math then my handy calculator above will do all the work for you. You might also be interested in my list of wattagefor most household devices.
Here's the formula to figure the cost of running a device:
If your device doesn't list wattage, but it does list amps, then just multiply the amps times the voltage to get the watts. For example:
(If you're outside North America, your country probably uses 220 to 240 volts instead of 120.)
You can't always trust the wattage printed on the device, because many devices don't use the full listed wattage all the time. For example, the compressor in a refrigerator doesn't run constantly, only sometimes, so you can't go by the listed wattage for a fridge. My calculator takes this into account by listing the average wattage for fridges. The most accurate way to find the average wattage of a device is to measure it with a watt-hour meter.
Exercise #1. Go get your electricity bill and see how many kilowatt hours you used last month.
Exercise #2. Assume that the lights in your kitchen and living room together use 400 watts. How much does it cost if the lights are on 24 hours a day, for a whole month? How much per year? Assume 15¢/kWh. (see answer)
• 400 watts x 24 hours/day x 30.5 days/month = 292,800 Total Watt-hours
• 292,800 Wh / 1000 Wh = 293 kwh
• 293 kWh x 15¢/kWh = $44/mo.; $528/yr.
Exercise #3. Assume your window AC uses 1440 watts. How much does it cost to run it continuously for a month? How much per year? Assume 15¢/kWh. (see answer)
• 1440 watts x 24 hours/day x 30.5 days/monh = 1,054,080 Total Watt-hours
• 1,054,080 Wh / 1000 Wh = 1,054 kWh
• 1,054 kWh x 15¢/kWh = $158/mo.; $1897/yr.
Watts vs. watt-hours
Many of my readers get confused about the difference between watts and watt-hours. Here's the difference:- Watts is the rate of use at this instant.
- Watt-hours is the total energy used over time.
Here's a question I frequently get, which makes no sense:
'You say that some device uses 100 watts. What period of time is that for?'
It's not for any period of time, because watts is a rate at that instant. One might as well ask:
'The speedometer in my car says I'm going 35 miles an hour. What period of time is that for?'
It's not for any period of time. You're going 35 miles an hour at that instant.
The difference is:
- We use watts to see how hungry a device is for power. (e.g., 100-watt bulb is twice as hungry as a 50-watt bulb.)
- We use watt-hours to see how much electricity we used over a period of time. That's what we're paying for.
So, just multiply the watts times the hours used to get the watt-hours. (Then divide by 1000 to get the kilowatt-hours, which is how your utility charges you.) Example: 100-watt bulb x 2 hours ÷ 1000 = 0.2 kWh.
Trivia The average U.S. household uses 920 kWh a month. (Dept. of Energy) The U.S. as a whole used nearly 4 trillion kWh in 2009. (DoE) About 37% was residential use. (DoE) On a peak day in 1999, California used 50,743,000 kilowatt-hours. Wikipedia has a list of electricity rates around the world. Despite the whining from some American consumers, the U.S. has some of the lowest electricity rates in the world (just like with its tax rates). |
How much does electricity cost?
The cost of electricity depends on:- where you live
- how much you use
- the time of year (summer rates are usually higher than winter)
- possibly when you use it (some utilities have lower rates in the evenings)
- who your provider is (every utility has different rates).
The electric company measures how much electricity you use in kilowatt-hours, abbreviated kWh. Your bill might have multiple charges per kWh (e.g., this bill has five different per-kWh charges) and you have to add them all up to get the total cost per kWh. Most bills have at least two per-kWh charges, one for supply (generating the electricity) and one for delivery(getting it from the power plant to your house).
Average rates
The national average rate for electricity is all but useless for two reasons:
- Electricity rates vary widely.They vary not only by region (e.g., an average of 7.5¢ in Idaho vs. 36¢ in Hawaii), but they also vary from the same utility. I found rates ranging from 12¢ to 50¢ per kWh from the same provider. The only way to know what you're actually paying is to check your bill carefully. You can't find out your own kWh rate by reading this web page.
- Electric rates are usually tiered, meaning that excessive use is billed at a higher rate. This is important because your savings are also figured for the highest tier you're in. For example, let's say you pay 10¢/kWh for the first 500 kWh, and then 15¢/kWh for use above that. If you normally use 900 kWh a month, then every kWh you save reduces your bill by 15¢. (Well, once you get your use below 500 kWh, then your savings will be 10¢ kWh, but you get the point.) When using my Savings Calculator above, you should generally choose the highest tier you're currently paying.
But for what it's worth (which is not much), the average residental electricity rate was 13¢/kWh in the U.S. for 2014. (from the DoE, table 5.3, which also has historical rates. Price data includes taxes.)
More on tiered rates
Because savings happen at the highest-billed tier, those writing about saving electricity generally should not use the average rate, since the savings rate will usually be higher. That's why I use a sample rate 15¢, instead of the average rate of 12¢.California has a ridiculously complicated way of figuring its tiers. First you have to find your 'baseline quantity' (different for every area, and for winter vs. summer) and then multiply that by the number of days in the billing cycle. For example, an all-electric (no gas) San Francisco household has baseline quantities of 11.1 for summer and 20.2 for winter. In a 31-day month, the baseline is 11.1 x 31 = 344 kWh for summer and 20.2 x 31 = 626 kWh for winter. Once you know the baseline, you can see the tiers, as follows (along with some sample pricing from PG&E as of January 2012):
- 12¢ / kWh - up to the baseline
- 14¢ / kWh - 101 to 130% of baseline
- 29¢ / kWh - 131 to 200% of baseline
- 33¢ / kWh - >200% of baseline
(Yes, I know that PG&E has petitioned to change to a 3-tier system...in the future. Feel free to let me know when that actually goes into effect.)
Regional data
Here are the averagerates for each state (Table 5.6.A.) as compiled by the DoE, but remember again that looking at average rates is all but useless. You really want to know your rate from your utility, and even then you should look for the rate you're paying in your highest tier, since that's the rate you'll save at through your conservation efforts.
Here's a link to the rates at PG&E (Pacific Gas & Electric), one of the larger providers.
Switch electric providers to lower your cost?
Until recently, no one had a choice about where they got their electricity from. There was only one company (or co-op, or public utility), and that was it. But recently, some states have allowed new providers to come in and compete, so depending on where you live, you might have the option to pick your provider now. The idea is that when there's competition, that results in lower prices for the consumer.
The reality is that due to the unique nature of electricity as a product, this competition hasn't resulted in very much potential savings so far, and isn't likely to do so in the future. In fact, in some cases electricity prices went up after deregulation. (WSJ, 2008) And whatever the potential savings from switching providers, in most cases it pales in comparison to the money you can save by washing in cold instead of hot, dialing up the thermostat in the summer, or using LED or CFL light bulbs. You almost always get greater savings from conservation, so please do that first before you look at changing providers. Only after you've made some progress at reducing your consumption is it time to look for another provider, which you can do at ElectricRate.com.
Demand Charges
Some utility companies impose an additional charge based on the maximum amount of electricity you draw at any one time. This is called a demand charge. The chart at right from Wisconsin Electric illustrates the concept. The shaded area is how much electricity you used, and you know you get charged for that. But the black bar on top is the demand, how much energy you 'demanded' at any given point throughout the day. If your utility company has a demand charge (ask them), then you can save money by spreading out your electrical use throughout the day. Running appliances one after the other rather than at the same time would reduce your demand. And better yet, running them when you're not using much electricity for other purposes (such as at night when the air conditioner is off) will reduce your demand even more.
Possibly cheaper in the evenings
Some utilities have cheaper rates in the evenings. (Check with them to find out.) That's because it's harder for them to reach peak demand during the day when everyone's running the AC. So they might charge less in the evenings to try to get you to move some of your consumption (like laundry machines) outside of those daytime hours. And even if your utility doesn't have cheaper rates at night, if your utility has a demand charge (see above), it could still pay to shift your laundry to the evenings, because running laundry + air conditioning at the same time results in a higher demand.
'Doesn't my ulitility want me to use more electricity so they can make more money?'
Most utilities in the U.S. are owned by their members (co-ops) or by the government. (source) In those cases there aren't any shareholders or owners demanding higher profits. And even when a utility is a traditional business, they're often regulated and can't just promote electric consumption willy-nilly. In any event, whether you trust or distrust your utility, you can still save energy by using the strategies listed on this website.
Smart meters are not overcharging you
In recent years utilities have replaced the old spinning-disc meters with new digital smart meters which radio in your usage,for the extremely obvious reasons: so they don't have to pay meter-readers to trudge through thousands of miles of neighborhoods each month, and so they can monitor demand better. Of course anti-government consipracy theorists have decided that the real reason behind smart meters is to spy on us and to overcharge us (the new meters supposedly register more usage than actually occurs).
Always the victims, it's always The Man trying to persecute and oppress us, isn't it? Whatever. And of course, since I won't tell the 'truth' about these meters, many of the Anti-Smart Meter Warriors for Freedom think that I'm in on the fix, being paid off by the utilities in order to buy my silence. Oh yeah, I'm rollin' in it.
»» Now let's examine how much electricity your appliances use. »»
Last update: February 2015
Nm3 is a common unit used in industry to refer to gas emissionsor
exchange. It stands for Normal cubic meter. 'Normal' is alwaysdependant on the individual circumstances of each gas, pressure,and use.
To convert Nm3 to a cubic foot of gas (under standardconditions),
multiply by 38.04.
Therefore, 1,000 Nm3/day = 1 kNm3/day = 38,040 cf/day.
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I don't know what does Nm3/h mean? Please help me. Thanks a lot! Read More
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You cannot because they are not comparable units. Read More
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suppose your line pressure is 2bar so m3/hr= Am3/hr(1+line pressure) and from m3/hr it can be converted to Nm3/hr using ideal gas law Read More
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NM3: NM3 stands for Normal meter cube and especially this unit is used gas/vapour application. NM3 is a constant value under the Varying Pressure and Temperature. NM3 is calculated if the Density and Mass of the gas/vapour is known. For Eg : In a pipeline, If Air is flowing at the rate of 1000M3/hr at the Pressure of 5Barg and at the temperature of 30degC, then Density of Air can be arrived from the corresponding… Read More
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Each kmole has a volume of 22,41272 Nm3 at normal state (1,01325 bar and 0°C). Read More
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1mL is 1cm3, and 1cm is 10^7nm so 1mL=1cm^3=10^21nm^3 Read More
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Am3 is an Actual Meter Cubed. The usual formula for gas volume calculations is Nm3 (Normal Meter Cubed) and uses the standard of 0 degrees Celsius and atmospheric pressure, whereas with Am3, the actual operating conditions are used for the calculation for higher accuracy. Read More
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In 4 degree celsius the density of water is high at the level . And it unit in SI is 1000kgm and in CGS 1gcm Read More
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Whoa. Let's take this slowly. -- One meter cubed (cubic meter) is the same amount of space as 1,000 litres. The newton doesn't belong here at all. -- A 'newton-meter' is a unit of energy, and has nothing to do with a volume of space. -- A 'newton meter cube' is a meaningless quasi-unit, with no physical significance. Read More
Convert from Sm3 to Nm3?
Both have applications in gas volume measurements. Nm3 is 'Normal cubic meter' 'Normal' is a set pressure and temperature which (just to make things difficult) differs between industries. Sm3 is'Standard cubic meter', a volume unit of measurement defined as follows: 'Cubic meter at a temperature of 15° Celsius and a pressure of 101.325 kPa (Kilopascal)'. So, to perform the conversion, you will have to take into account the industry definition of 'Normal' and compute Sm3… Read More
Is Newton meter cubed equal to normal meter cubed?
Nm3 is a measure for volume of gases, in cubic meter, under special conditions of pressure (1 atm) and temperature ( zero degrees centigrade). The name for this unity is Normal Cubic Meter. It is not Newton meter cubed. Read More
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flow/ valve(Nm3/hr) = 4.73*Kv*absolute pressure* on time* no. of valve firing*3600/ off time. Kv = Flow coefficient of pulse valve. not understood pls let me know... Read More
Conversion of kg per hr into nm3 per hr?
You cannot convert kilograms per hour (kg/hr) into nanometers cubed per hour (nm3/hr). The kilogram is a measure of mass or weight while the cubic nanometer is a measure of volume. There is no direct conversion, unless you specify the density of the material involved. Read More
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You could use the following Rule of Thumb: Multiply the square of the inside diameter, in inches, by the gauge pressure, in psi; multiply this by 0.372; the answer is the approximate number of cubic ft of gas (standard conditions) in 1,000 ft of line, e.g 7 inch ID pipeline, 8km long, operating at 65 barg: 8 km = 26246 ft = 26.246 kft 65 Bar = 942.7 psi so, 7 x 7 x 942.7… Read More
Convert kWh into Nm3?
As I read the question, I think I know what 'kWh' is (are), but I'm not so sure about 'Nm3' . I'm assuming that 'kWh' means 'kilowatt-hour', a unit of energy equal to 3,600,000 joules. I'm having trouble recognizing 'Nm3' as a unit of energy, and if it's not a unit of energy, then it has no relationship to kilowatt-hours. Read More
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Basically, calorific value of any sludge depends on its constitution. Since sludge is not defined composition wise, its accurate calorific value doesn't exist. And another important factor which affects the calorific value is the end product that's generated out of sludge. eg if biogas is generated, then calorific value would be 22,000 kJ/Nm3 (http://www.currenta.com/pages/1577/life_2008_final_engl.pdf) topic open for discussion!! Read More
That I'm pretty?
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