What Is a Kilowatt-Hour (kWh)? Meaning, kW vs kWh and Cost

Every electric bill in the United States is measured in kilowatt-hours, yet few people can say exactly what one is. A kilowatt-hour (kWh) is simply a quantity of energy: the amount used by something drawing 1,000 watts for one hour. Once you understand it, you can work out what any appliance costs to run, compare electricity plans, size solar panels and estimate what an electric car adds to your bill. This guide explains the unit, the difference between kW and kWh, what one kWh actually does, and how much it costs across the US. To convert your own numbers, try the kWh calculator.

What is a kilowatt-hour?

A kilowatt-hour is a unit of energy equal to 1,000 watts of power sustained for one hour. It equals 3,600,000 joules (3.6 megajoules) and is the standard unit utilities use to measure and bill electricity. The joule is the SI unit of energy, as defined in the BIPM SI Brochure; the kWh is a non-SI unit that converts to it exactly, since 1 kW × 3,600 s = 3.6 MJ (NIST SP 811).

Break the name into its parts:

• A watt (W) is a unit of power, the rate at which energy flows. It is named after the Scottish engineer James Watt (1736–1819); see the history section below.
• A kilowatt (kW) is 1,000 watts.
• An hour is the length of time that power flows.

Put together, a kilowatt-hour is power multiplied by time. That’s why a 100-watt device and a 1,000-watt device can both use 1 kWh: the first takes 10 hours, the second just one.

The formula is:

kWh = watts × hours ÷ 1,000

A 1,500 W space heater running for 4 hours uses 1,500 × 4 ÷ 1,000 = 6 kWh. Our watts to kWh converter does this math for any device.

How many watts is a kilowatt-hour?

A kilowatt-hour is not a number of watts: it is 1,000 watts used for one hour, which equals 1,000 watt-hours (Wh). Watts measure power, the rate of use; watt-hours and kilowatt-hours measure energy, the amount used. So 1 kWh could be 1,000 W for 1 hour, 500 W for 2 hours or 100 W for 10 hours.

Power draw	Time to use 1 kWh
100 W	10 hours
250 W	4 hours
500 W	2 hours
1,000 W (1 kW)	1 hour
2,000 W	30 minutes
4,000 W	15 minutes

The rule is hours = 1,000 ÷ watts. The same logic answers “how many kilowatts is a kilowatt-hour”: 1 kW sustained for one hour.

Larger quantities use bigger prefixes. A megawatt-hour (MWh) is 1,000 kWh, a gigawatt-hour (GWh) is a million kWh, and a terawatt-hour (TWh) is a billion kWh. Power plants, utilities and national statistics agencies such as the US Energy Information Administration (EIA) usually report in MWh, GWh or TWh.

kW vs kWh: what is the difference?

A kilowatt (kW) measures power, how fast energy is used at a given moment; a kilowatt-hour (kWh) measures energy, the total amount used over time. kW is like speed in miles per hour; kWh is like miles driven.

	Kilowatt (kW)	Kilowatt-hour (kWh)
What it measures	Power (a rate)	Energy (an amount)
Car analogy	Speed (mph)	Distance (miles)
Where you see it	Appliance labels, solar system size, EV charger rating, generator size	Electric bill, battery capacity, solar production, EV efficiency
Example	A 7.2 kW home EV charger	That charger running 2 hours delivers 14.4 kWh
Conversion	1 kW = 1,000 W	1 kWh = 1 kW for 1 hour = 3.6 MJ

The two are linked by time:

• kWh = kW × hours
• kW = kWh ÷ hours

People mix them up constantly. A “10 kW solar system” describes its peak power output, not how much energy it makes; the energy it produces over a year is measured in kWh. Likewise, a home battery is sized in kWh (how much it stores) and in kW (how fast it can deliver). To convert power units, use the kW to watts converter.

How does a kilowatt-hour compare with other energy units?

One kWh equals 3.6 megajoules, 1,000 watt-hours and about 3,412 British thermal units (Btu), so it can be converted to any other energy unit with a fixed factor. Which unit you see depends on the industry.

• Watt-hours (Wh). Small batteries, such as phone and laptop packs, are often rated in Wh. A 100 Wh laptop battery stores 0.1 kWh.
• Joules (J). Scientists use the joule, the SI unit of energy. One kWh is 3.6 million joules.
• British thermal units (Btu). Natural gas, furnaces and air conditioners are often rated in Btu. The EIA converts electricity at about 3,412 Btu per kWh, which lets you compare an electric heat pump with a gas furnace on equal terms.
• Therms. Gas bills often use the therm, which is 100,000 Btu, or roughly 29.3 kWh.
• Milliamp-hours (mAh) and amp-hours (Ah). These measure electric charge, not energy. Multiply by the battery voltage to get watt-hours, then divide by 1,000 for kWh.

Our BTU to kWh converter and mAh to kWh converter handle these conversions for you.

What does 1 kWh of electricity run?

One kWh will run a 50-watt laptop for about 20 hours, a 1,000-watt coffee maker for one hour, or a large clothes dryer for as little as 12 minutes. The higher a device’s wattage, the faster it uses a kWh.

The table uses typical nameplate wattage ranges published by Virginia Cooperative Extension in its appliance energy guide. Nameplate wattage is the maximum draw; actual use is often lower because many appliances cycle on and off.

Device	Typical wattage	Time to use 1 kWh	Cost per hour at 18.2¢/kWh
Laptop	About 50 W	About 20 hours	0.9¢
Desktop PC (awake)	About 120 W	About 8.3 hours	2.2¢
Computer monitor (awake)	About 150 W	About 6.7 hours	2.7¢
Clothes washer	350–500 W	2–2.9 hours	6.4–9.1¢
Microwave	750–1,100 W	55–80 minutes	13.7–20.0¢
Coffee maker	900–1,200 W	50–67 minutes	16.4–21.8¢
Dishwasher	1,200–2,400 W	25–50 minutes	21.8–43.7¢
Clothes dryer	1,800–5,000 W	12–33 minutes	32.8–91.0¢
Level 2 home EV charger	Up to about 7,200 W (DOE)	About 8 minutes	Up to $1.31

Sources: Virginia Cooperative Extension BSE-301 (wattage ranges); US DOE Alternative Fuels Data Center (home Level 2 charger power). Cost assumes 18.2¢/kWh and full nameplate draw.

For an electric car, one kWh goes a long way. Popular 2026 EVs are rated by the EPA at about 24 to 33 kWh per 100 miles, so each kWh from the wall moves the car roughly 3 to 4 miles. Our guide to the cost to charge an electric car turns that into dollars.

How many kWh does the average US home use?

The average US residential customer used 865 kWh of electricity per month in 2024, about 28 to 29 kWh per day, according to the EIA. That was 2% more than in 2023.

Use varies widely by state and climate. The EIA notes that households in Louisiana used more than twice as much grid electricity as those in Hawaii or California in 2024, largely because of air conditioning and electric heating. Hawaii still had the highest average monthly bill, at $213, because its price per kWh is so high; Utah had the lowest, at $89 (EIA, 2024).

Your own use depends on:

• Heating and cooling. Electric furnaces, heat pumps and central air conditioning are usually the largest loads in a home.
• Water heating. An electric water heater runs every day of the year.
• Home size and number of people. More rooms and more occupants mean more lighting, laundry and devices.
• Electric vehicles. Driving 1,000 miles a month in an EV rated at 27 to 31 kWh per 100 miles adds about 270 to 310 kWh.
• Season. Bills typically peak in summer in hot states and in winter in homes with electric heating.

What uses the most electricity in a house?

Air conditioning is the largest single use of electricity in US homes, at 19% of residential electricity in 2020, followed by space heating (12%) and water heating (12%), according to the EIA, based on its Residential Energy Consumption Survey. Lighting and refrigerators are the next largest uses. The shares shift from year to year with the weather, so the biggest savings usually come from heating, cooling and hot water rather than small electronics.

To estimate your household’s use appliance by appliance, try the electricity cost calculator. See how to lower your electric bill for what each saving is worth.

How much is a kilowatt-hour?

The average US home paid 18.16¢ per kWh in August 2026 (EIA, preliminary), but state averages ranged from 12.87¢ in Louisiana to 47.18¢ in Hawaii. The average price rose from 16.0¢ in 2023 to 16.5¢ in 2024 (EIA).

State	Residential price per kWh, Aug 2026 (EIA)	Cost of 865 kWh (2024 US average month)
Hawaii	47.18¢	$408
Massachusetts	30.48¢	$264
California	29.75¢	$257
New York	28.65¢	$248
Connecticut	24.51¢	$212
US average	18.16¢	$157
Texas	15.91¢	$138
Florida	14.99¢	$130
Washington	14.63¢	$127
Idaho	13.37¢	$116
North Dakota	13.31¢	$115
Louisiana	12.87¢	$111

The third column holds usage constant to show the effect of price alone; real bills also reflect how much each state’s households use. Prices also vary between utilities within a state, and many utilities change rates by season or time of day. This site uses 18.2¢ (the rounded August 2026 national average) as its default in every calculator.

Prices are shaped by fuel costs, transmission and distribution spending, weather and the local generation mix. States with abundant hydropower, such as Washington and Idaho, tend to have lower rates. Learn more about how each resource works in our overview of renewable energy sources.

History of the watt and the kilowatt-hour

The kilowatt-hour grew out of two 19th-century needs: a name for the unit of power, which honored James Watt, and a way for the first electric utilities to bill customers for the energy they used. Both were settled between 1882 and 1889, and the watt became part of the International System of Units (SI) in 1960.

James Watt (1736–1819) never measured electricity; he made his name improving the steam engine, patenting a separate condenser in 1769, and popularized horsepower as a measure of engine output. A century later, electrical engineers wanted names for their practical units. In August 1882 C. William Siemens proposed the “watt” in his presidential address to the British Association for the Advancement of Science, defining it as the power of one ampere flowing through one volt. At the second International Electrical Congress, on 31 August 1889, the joule was officially adopted alongside the watt.

Billing needed a meter. Thomas Edison’s 1882 Pearl Street system in Manhattan used a chemical meter: current passed through jars of zinc sulfate, and the utility weighed the zinc plated onto the electrodes to estimate use. In 1888 Westinghouse engineer Oliver Shallenberger built an alternating-current meter that read out directly (US Patent 449,003), the ancestor of the spinning-disk meters that recorded household kWh for most of the 20th century. When the 11th General Conference on Weights and Measures founded the SI in 1960, the watt and joule became its units of power and energy; the kWh stayed in use because it matches how people buy electricity.

Year	Milestone	Source
1769	James Watt patents the separate condenser for steam engines	Wikipedia
1882	Edison’s chemical (zinc-plating) meter used on the Pearl Street system	The Henry Ford
1882	Siemens proposes the watt as a unit (August, British Association)	Wikipedia
1888	Shallenberger invents his AC watt-hour meter (patent 449,003 granted 1891)	ETHW
1889	Second International Electrical Congress adopts the joule and watt (31 August)	Wikipedia
1908	London conference adopts the “international watt”	Wikipedia
1960	11th CGPM establishes the SI, with the watt as the unit of power	NIST SP 330

How to read kWh on your electric bill

Your bill shows how many kWh your meter recorded during the billing period and the price charged for them; dividing the bill total by the kWh gives your true all-in price per kWh. It takes five steps.

1. Find the usage line. Look for “kWh used,” “energy usage” or “consumption.” Many bills show a current and previous meter reading; the difference is your kWh.
2. Check the billing period. Most cover about 30 days. Divide kWh by days to get daily use.
3. Separate fixed and variable charges. A fixed “customer” or “service” charge is billed every month regardless of use. Energy (supply) and delivery (distribution) charges are usually priced per kWh.
4. Look for time-of-use or tiers. Some plans charge different prices by time of day (peak and off-peak) or raise the price after a usage threshold.
5. Calculate your price. Divide the total bill by total kWh for your all-in price, or divide only the per-kWh charges by kWh for your marginal price, the cost of using one more kWh.

Your marginal price matters most when you’re deciding whether to add a load like an EV or a heat pump, because fixed charges don’t rise when you use more. It’s also what solar panels save you, since every kWh they produce is a kWh you don’t buy.

How are kilowatt-hours connected to solar power?

Solar panels are rated in kW of peak power, but what they produce, and what saves you money, is energy in kWh. A 1 kW array producing at full rated output for one hour generates 1 kWh.

In practice panels rarely run at full output all day. Production rises and falls with the sun’s angle, clouds, temperature, shading and the season, so annual output depends heavily on location. That’s why solar quotes list both the system size in kW and the expected yearly production in kWh.

Thinking in kWh makes solar easy to size:

• Add up your annual kWh from twelve months of bills.
• Decide what share of that you want solar to cover.
• Use the solar panel calculator to estimate how many kW of panels your location needs to produce those kWh.

Batteries work the same way. An off-grid home sizes its battery bank in kWh to cover a day or more of use, and its panels in kW to refill it; see our guide to the off-grid solar system. For the physics of turning sunlight into kWh, read how solar panels work, and for costs and output, our solar energy guide. Every kWh from the sun, wind or water is a step toward a grid powered by renewable energy.

Scientific references

The definitions and conversion factors on this page come from these metrology standards and references:

1. Bureau International des Poids et Mesures (2019). The International System of Units (SI), 9th edition (SI Brochure). BIPM SI Brochure
2. Newell, D. B., & Tiesinga, E. (Eds.) (2019). The International System of Units (SI). NIST Special Publication 330, 2019 edition. doi:10.6028/NIST.SP.330-2019
3. Thompson, A., & Taylor, B. N. (2008). Guide for the Use of the International System of Units (SI). NIST Special Publication 811. doi:10.6028/NIST.SP.811e2008
4. US Energy Information Administration. “British thermal units (Btu),” Energy Explained (conversion factor 1 kWh = 3,412 Btu). EIA
5. Shallenberger, O. B. (1891). “Meter for alternating electric currents.” US Patent 449,003. Google Patents

Bottom line

A kilowatt-hour is 1,000 watts used for one hour, the unit your utility uses to bill you. kW measures how fast energy is used; kWh measures how much. The average US home used 865 kWh a month in 2024, and the average price was 18.16¢ per kWh in August 2026, though your state’s rate may be far higher or lower. Multiply watts by hours, divide by 1,000 and multiply by your rate, and you can price any appliance, an electric car or the value of a solar system. Start with the kWh calculator, then see what that means for driving in the cost to charge a Tesla. Once you think in kWh, every electricity decision in your home becomes simple arithmetic, including how much renewable energy you would need to cover it.