A kilowatt (kW) measures power, the rate at which electricity is used or produced at one moment. A kilowatt-hour (kWh) measures energy, the total amount used over time: 1 kWh is 1 kW running for 1 hour. Think of kW as speed and kWh as distance. Your utility bills you for the distance, and in 2025 the average US home paid 17.30 cents for each kWh (EIA).
This guide explains both units, shows how to convert kW to kWh with worked examples, lists typical appliance wattages, and covers the conversions people search for most: watts, Wh, MWh, BTU, joules and amp-hours. It also shows what a kWh costs and how much CO₂ it produces.
kWh vs kW: power vs energy
Power is how fast energy flows. Energy is how much has flowed in total. The US Energy Information Administration (EIA) defines one kilowatt as 1,000 watts, and one kilowatt-hour as one kilowatt generated or used for one hour.
A car’s speedometer shows miles per hour, and the odometer shows miles traveled. A kW figure is the speedometer reading. A kWh figure is the odometer reading.
| kW (kilowatt) | kWh (kilowatt-hour) | |
|---|---|---|
| What it measures | Power (a rate) | Energy (a quantity) |
| Car analogy | Speed, in mph | Distance, in miles |
| In smaller units | 1,000 watts | 1,000 watt-hours |
| Where you see it | Appliance labels, solar system size, charger speed | Electricity bills, battery capacity, meter readings |
What is a kWh?
A kWh (kilowatt-hour, which EIA writes as “kilowatthour”) is the standard unit of electrical energy. It means 1,000 watts sustained for one hour, or any combination of power and time that multiplies out to the same total.
So what does kWh mean in practice? A 1,000-watt microwave running for one hour uses 1 kWh. So does a 100-watt device running for 10 hours, or a 2,000-watt heater running for 30 minutes.
The average US household uses about 10,500 kWh of electricity per year (EIA, 2020 data). That is 10,500 ÷ 12 = 875 kWh per month. For a breakdown by home size and state, see how many kWh a house uses.
kW to kWh: how is kWh calculated?
To figure kWh, multiply power by time:
kWh = kW × hours
You cannot convert kW to kWh without knowing the hours, just as you cannot turn 60 mph into miles without knowing how long you drive.
Three worked examples
- Space heater: a 1.5 kW portable heater running for 4 hours uses 1.5 × 4 = 6 kWh.
- TV: a 120-watt flat screen is 120 ÷ 1,000 = 0.12 kW. Over 5 hours it uses 0.12 × 5 = 0.6 kWh.
- Light bulb (EIA’s own example): a 40-watt bulb is 0.04 kW. Over 5 hours it uses 0.04 × 5 = 0.2 kWh.
Watts to kWh
Most appliance labels show watts, not kilowatts. The formula becomes:
kWh = watts × hours ÷ 1,000
How many watts in a kWh?
Strictly, none, because watts and kWh measure different things. But 1 kWh equals 1,000 watt-hours: 1,000 watts used for one hour.
Turn kWh into CO₂ in one step. Pick your country, enter your kWh and see the emissions behind it. Open the free kWh to CO₂ Calculator
Typical appliance wattage and kWh per hour
The table below uses typical wattages published by Virginia Cooperative Extension in its home energy series. They are typical values. Your appliance’s nameplate is the better number, and many appliances cycle on and off, so real use is often lower.
The kWh column assumes one full hour of running. The cost column multiplies that by the 2025 US average residential price of 17.30 cents per kWh (EIA).
| Appliance | Typical wattage | kWh for 1 hour of use | Cost for 1 hour at 17.30¢/kWh |
|---|---|---|---|
| Laptop | 50 W | 0.05 | 0.9¢ |
| Flat screen TV | 120 W | 0.12 | 2.1¢ |
| Microwave oven | 750–1,100 W | 0.75–1.1 | 13.0–19.0¢ |
| Portable heater | 750–1,500 W | 0.75–1.5 | 13.0–26.0¢ |
| Hair dryer | 1,200–1,875 W | 1.2–1.875 | 20.8–32.4¢ |
| Dishwasher | 1,200–2,400 W | 1.2–2.4 | 20.8–41.5¢ |
| Clothes dryer | 1,800–5,000 W | 1.8–5.0 | 31.1–86.5¢ |
| Water heater (40 gallon) | 4,500–5,500 W | 4.5–5.5 | 77.9–95.2¢ |
kWh conversions: Wh, MWh, BTU, joules and amp-hours
A kWh is an energy unit, so it converts cleanly to any other energy unit. The BTU figure is EIA’s standard conversion factor. The joule figure follows from the definition of a watt as one joule per second: 1,000 watts × 3,600 seconds = 3,600,000 joules.
| 1 kWh equals | To convert to kWh |
|---|---|
| 1,000 Wh (watt-hours) | Wh ÷ 1,000 |
| 0.001 MWh (megawatt-hours) | MWh × 1,000 |
| 3,412 BTU | BTU ÷ 3,412 |
| 3,600,000 joules (3.6 MJ) | joules ÷ 3,600,000 |
Wh to kWh
Divide by 1,000. A 500 Wh power station holds 500 ÷ 1,000 = 0.5 kWh.
MWh to kWh and kWh to MWh
How many kWh in a MWh? Exactly 1,000. To go from kWh to MWh, divide by 1,000. The average household’s 10,500 kWh per year is 10.5 MWh. For scale, one modern wind turbine makes thousands of MWh a year, as shown in how much electricity a wind turbine produces.
kWh to BTU
Multiply by 3,412. A 6 kWh heater session delivers 6 × 3,412 = 20,472 BTU of heat.
Joules to kWh
Divide by 3,600,000. For megajoules, divide by 3.6. So 18 MJ ÷ 3.6 = 5 kWh.
Ah to kWh
Amp-hours measure charge, not energy, so you need the battery voltage: kWh = Ah × volts ÷ 1,000. A 100 Ah battery at 12 volts stores 100 × 12 ÷ 1,000 = 1.2 kWh. The same 100 Ah at 48 volts stores 4.8 kWh.
How much is a kWh?
The US average residential price was 17.30 cents per kWh in 2025 (EIA annual average). Commercial customers paid 13.41 cents and industrial customers 8.62 cents. In July 2026, the latest month EIA has published, the residential average was 18.31 cents per kWh, up 4.9% from July 2025.
At the 2025 average, a household using 875 kWh per month pays 875 × $0.1730 = $151.38 for the energy. Prices vary widely between states, so check electricity cost by state for your local rate.
Where kW and kWh show up
On your electricity bill
Residential bills are built around the energy charge: kWh used × price per kWh. Many commercial and industrial bills add a demand charge, which is priced per kW and based on the highest power drawn during the billing period, usually measured over a short interval.
How to read a kWh meter
A meter counts kWh like an odometer. It shows a running total, so your use for a period is the current reading minus the previous one. If last month’s reading was 45,210 and today’s is 46,085, you used 46,085 − 45,210 = 875 kWh. On older dial meters, take the lower number when a pointer sits between two digits.
On solar systems
Solar system size is quoted in kW: the peak power the panels can deliver in ideal test conditions. What you save money on is the kWh the system produces. A 7 kW array running at full output for 4 hours makes 7 × 4 = 28 kWh. Real output depends on location and season, which the solar savings calculator estimates.
On EV batteries and chargers
An EV battery’s capacity is in kWh, the size of the tank. A charger’s speed is in kW, how fast it fills. As an illustration, adding 60 kWh with an 11 kW home charger takes about 60 ÷ 11 = 5.5 hours, while a 150 kW fast charger holding full power would need 60 ÷ 150 = 0.4 hours, or 24 minutes. Real sessions run longer because charging slows as the battery fills. See how many kWh it takes to charge a Tesla for model-level numbers.
On home batteries
Home batteries carry both ratings, and you need both. The kWh rating says how much energy is stored. The kW rating says how many appliances it can run at once. A 13.5 kWh battery feeding a steady 1.5 kW load lasts 13.5 ÷ 1.5 = 9 hours, but only if its kW rating covers your peak load.
kVA vs kW
Generators, transformers and UPS units are often rated in kVA (kilovolt-amperes). kVA is apparent power: volts × amps ÷ 1,000. kW is real power, the part that does useful work. The two are linked by the power factor:
kW = kVA × power factor
A 10 kVA generator feeding a load with a 0.8 power factor delivers 10 × 0.8 = 8 kW. For purely resistive loads such as heaters, the power factor is 1 and kVA equals kW.
Common mistakes with kW and kWh
- “kW per hour.” A kW already is a rate. Saying a heater uses “1.5 kW per hour” is like saying a car drives “60 mph per hour”. The heater draws 1.5 kW and uses 1.5 kWh each hour.
- “kWh/h.” kWh divided by hours is just kW, a long way of writing average power.
- Using kW for battery size. A “10 kW battery” tells you its power output, not how long it lasts. Capacity is always kWh.
- Wrong capitalization. The correct form is kWh: lowercase k for kilo, capital W for watt (named after James Watt), lowercase h for hour.
kWh to CO₂: how much carbon is in a kWh?
The US grid emitted an average of 767.2 pounds of CO₂ per MWh of electricity generated in 2023, according to EPA’s eGRID, the latest edition. Per kWh that is 767.2 ÷ 1,000 = 0.767 lb, or 0.767 × 0.4536 = 0.348 kg. EIA’s own estimate for 2023 is slightly higher, at about 0.81 lb per kWh.
Worked example: an average household using 10,500 kWh per year causes 10,500 × 0.767 = 8,054 lb of CO₂. That is 8,054 × 0.4536 = 3,653 kg, or about 3.65 metric tons per year.
The national figure is an average. The same kWh carries very different emissions depending on the local power mix. You can compare the electricity mix and carbon intensity by country, or read emission factors explained to see how these per-kWh numbers are built. The kWh to CO₂ calculator does the math for your country.
Frequently asked questions
Is 1 kW equal to 1 kWh?
No. 1 kW is a rate of power and 1 kWh is an amount of energy. A 1 kW device uses 1 kWh only if it runs for exactly one hour.
How many kWh is 1 kW for 24 hours?
1 kW × 24 hours = 24 kWh. At the 2025 US average residential price of 17.30 cents per kWh, that costs 24 × $0.1730 = $4.15.
How many kWh does a house use per day?
The average US household uses about 10,500 kWh per year (EIA, 2020 data), which is 10,500 ÷ 365 = 28.8 kWh per day.
What is the difference between MW and MWh?
It is the same split at a larger scale. A megawatt (MW) is 1,000 kW of power, and a megawatt-hour (MWh) is 1,000 kWh of energy.
Sources
- EIA: Measuring electricity
- EIA: Electricity prices and factors affecting prices
- EIA: Electricity Monthly Update, July 2026
- EIA: Energy conversion calculators (1 kWh = 3,412 BTU)
- EIA: Electricity use in homes
- EPA: eGRID summary data
- Virginia Cooperative Extension: Estimating appliance and home electronic energy use
About the author
Georgi Todorov is an eco activist and entrepreneur. He runs Ecoki, where he builds free tools and guides that help small businesses measure and cut their carbon footprint.