What is a kilowatt-hour (kWh)?
A kilowatt-hour (kWh) is the unit of energy your electric utility bills you for. It equals the energy used by a 1,000-watt (1 kW) appliance running for one hour. Equivalently, a 100 W device left on for 10 hours uses 1 kWh, and a 2,000 W device run for 30 minutes also uses 1 kWh. In the US, one kWh of residential electricity costs about 18.56¢ on average (March 2026, EIA).
Watts measure power; kWh measure energy used
Watts tell you how fast a device draws electricity (its power). A kilowatt-hour tells you how much energy it has used over time. To get kWh you multiply power by time:
kWh = (watts ÷ 1000) × hours
Examples: how long it takes to use 1 kWh
| Device | Power | Time to use 1 kWh | Cost of 1 kWh @ 18.56¢ |
|---|---|---|---|
| LED bulb | 10 W | 100 hours | $0.19 |
| Laptop | 50 W | 20 hours | $0.19 |
| Fridge (avg draw) | 150 W | ~6.7 hours | $0.19 |
| Microwave | 1,000 W | 1 hour | $0.19 |
| Space heater | 1,500 W | 40 minutes | $0.19 |
Frequently asked questions
What is a kilowatt-hour?
A kilowatt-hour (kWh) is the amount of energy used by a 1,000-watt (1 kW) appliance running for one hour. It is the unit electric utilities use to bill you. A 100 W bulb left on for 10 hours also uses 1 kWh.
How much does 1 kWh cost?
In the US, 1 kWh of residential electricity costs about 18.56¢ on average (EIA, March 2026), though it ranges from under 12¢ to over 42¢ depending on the state and utility.
How many kWh does a house use?
A typical US home uses roughly 850–950 kWh per month (about 10,000–11,000 kWh a year), but this varies enormously with home size, climate, heating fuel and whether you charge an EV.
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Last updated: 2026-06-20