A kilowatt-hour is the unit your electric utility uses to measure — and bill — the energy you use. Almost everyone has seen "kWh" on a bill without being told what it means. The definition is simpler than it looks, and getting it straight makes your whole bill readable.
The confusion usually comes from mixing up three related terms: watts, kilowatts, and kilowatt-hours. Two of them measure power (how fast you're using energy) and one measures energy (how much you used over time). This guide separates them cleanly, with concrete examples, then shows how a kWh turns into the number on your bill.
The short answer: what a kWh is
A kilowatt-hour (kWh) is the amount of energy used by running 1,000 watts of power for one hour.
So a 1,000-watt appliance running for one hour uses 1 kWh. A 100-watt light bulb left on for 10 hours also uses 1 kWh (100 watts × 10 hours = 1,000 watt-hours = 1 kWh). It's the standard unit electric companies bill you in — your rate is a price per kWh, and your monthly charge is that rate multiplied by the kWh you used.
That's the whole concept. The rest of this guide unpacks the pieces.
Watt vs. kilowatt vs. kilowatt-hour
These three terms trip people up because they sound alike but measure different things.
Watt (W) — the rate of energy use
A watt measures power: how fast a device uses energy at any moment. A device's wattage tells you its draw, not its total consumption. A 60-watt bulb draws 60 watts whenever it's on; a 1,500-watt space heater draws 1,500 watts while running. Think of watts like the speed on a car's speedometer — a rate, not a distance.
Kilowatt (kW) — just 1,000 watts
A kilowatt is simply 1,000 watts. It's the same kind of measurement as a watt (a rate of power), just a larger unit used for bigger loads. A 1,500-watt heater is a 1.5 kW heater. The "kilo" prefix means 1,000, exactly as it does in kilogram or kilometer.
Kilowatt-hour (kWh) — energy used over time
A kilowatt-hour measures energy: power multiplied by time. This is the one that matters on your bill, because it captures how much you actually used, not just how fast. Running 1 kW for 1 hour = 1 kWh. Running 1 kW for 2 hours = 2 kWh. If watts are the speedometer, a kWh is the odometer — the total distance traveled.
The formula is straightforward: kWh = (watts ÷ 1,000) × hours used. A 1,500-watt heater run for 4 hours uses (1,500 ÷ 1,000) × 4 = 6 kWh.
How many watts are in a kilowatt?
There are 1,000 watts in a kilowatt. It's a fixed conversion, like 100 centimeters in a meter:
- 1 kilowatt (kW) = 1,000 watts (W)
- 500 watts = 0.5 kW
- 2,400 watts = 2.4 kW
A common follow-up: is a kilowatt the same as a kilowatt-hour? No. A kilowatt (kW) is a rate of power; a kilowatt-hour (kWh) is energy used over time. A 1 kW appliance running for 1 hour uses 1 kWh — the kW is what it draws, the kWh is what it consumed. Your bill is in kWh because the utility charges you for energy used, not for the instantaneous rate.
How a kWh shows up on your electric bill
Your electric bill charges you in kilowatt-hours. Two numbers drive the supply portion of your bill: the kWh you used and your rate per kWh. Multiply them together and you have your supply cost.
For example, a household that uses 900 kWh in a month at a rate of 16¢/kWh pays about $144 for supply (900 × $0.16). Use more kWh, or pay a higher rate per kWh, and the number rises — those are the only two levers. (Your bill also includes delivery charges and fees from your utility, which are separate from the supply rate.)
To turn this from theory into your actual numbers, run your usage through our electricity cost calculator — it converts an appliance's wattage and hours into kWh and dollars for you. For a line-by-line walkthrough of the rest of the bill, see our guide to understanding your electricity bill.
How much does a kWh cost — and what's a "good" rate?
The U.S. residential average is roughly 16 to 17 cents per kilowatt-hour (EIA), but the real answer is: it depends heavily on where you live. State averages range from around 11¢ in the cheapest states to 40¢+ in Hawaii. A rate that's high in one market is normal in another, so there's no single national "good" number.
A more useful way to judge a rate is against your own market:
- In a regulated state, your rate is set by your utility and the state commission — "good" mostly means using fewer kWh, since you can't shop the rate.
- In a deregulated state (where you can choose your supplier — Texas, Pennsylvania, Ohio, and about a dozen others), a good rate is one at or below your utility's default rate. Competitive suppliers often price below that default, so the benchmark is your local floor, not a national figure.
If you're in a deregulated state and want to know whether your rate is competitive, our guide on how to choose an electricity company explains how to read a rate against the local default before you commit.
How many kWh do common appliances use?
Putting real numbers to a kWh makes it concrete. A few everyday examples, at the U.S. average rate:
- Refrigerator: A modern fridge uses about 440 kWh per year — roughly 1.2 kWh a day, or about $6 a month. An older model can use well over 700 kWh a year. Refrigerator cost calculator
- Central air conditioner: A central AC can use around 600 kWh in a peak cooling month — roughly $100 — because it runs for many hours. Air conditioner cost calculator
- Clothes dryer: A standard electric dryer uses about 3 kWh per load, or roughly 90 kWh a month (about $15) for a typical household. Dryer cost calculator
The pattern: a device's total kWh depends on both its wattage and how many hours it runs. A high-wattage appliance used briefly can cost less than a modest one running constantly — which is exactly why a refrigerator that's never "loud" still lands among your biggest annual energy users. If your bill is higher than these examples suggest it should be, our guide to why your electric bill is so high walks through the usual causes.
FAQ
How many watts are in a kWh?
This question mixes two different units, which is the heart of the confusion. A watt is a rate of power; a kWh is energy used over time. The cleaner question is "how many watts are in a kilowatt," and the answer is 1,000. To get a kWh, you run 1,000 watts for one hour — so a kilowatt-hour represents 1,000 watt-hours of energy, not 1,000 watts.
How much does 1 kWh cost?
About 16 to 17 cents on average in the United States (EIA), but it varies widely by state — from roughly 11 cents in the cheapest states to over 40 cents in Hawaii. To find your own price, look for the supply rate on your electric bill, listed as a price per kWh. Your supply charge is that rate multiplied by the kWh you used during the billing period.
What is a good price per kWh?
There's no single national number, because rates vary so much by state. A better benchmark is your local market. In a deregulated state, a good rate is one at or below your utility's default ("price to compare") rate — competitive suppliers often price below it. In a regulated state, you can't shop the rate, so a "good" outcome comes from using fewer kWh. Always compare a rate to your own area's default, not to a national average.
Is a kW the same as a kWh?
No. A kilowatt (kW) measures power — the rate at which energy is used. A kilowatt-hour (kWh) measures energy — the total amount used over time. A 1 kW appliance running for one hour uses 1 kWh; running for two hours uses 2 kWh. The kW describes how fast it draws power; the kWh describes how much it consumed. Your electric bill is measured in kWh because you're charged for energy used, not for the instantaneous draw.
How do I calculate the kWh an appliance uses?
Use this formula: kWh = (watts ÷ 1,000) × hours used. Find the appliance's wattage (often on a label or in the manual), divide by 1,000 to get kilowatts, then multiply by the number of hours it runs. A 1,500-watt heater run for 4 hours uses (1,500 ÷ 1,000) × 4 = 6 kWh. Multiply that by your rate per kWh to get the cost. Our electricity cost calculator does this math automatically.